fix(enrollment): restore working enrollment issue form and repair corrupted templates

The public "Begin the Adventure" link pointed at start-here-roadmap.yml,
which failed YAML parsing because a bulk edit on May 17 injected stray
column-0 "hidden: true" lines into 21 workshop issue templates (plus an
unsupported top-level "hidden" key in 40 files across the workshop and
learning-room template sets). GitHub cannot render an invalid issue form,
so enrollees got a blank issue with only the prefilled title - reported
by a learner on the BITS list on July 4.

- Remove every stray "hidden: true" line; all 54 templates now parse and
  contain only keys permitted by GitHub issue forms syntax
- Add .github/ISSUE_TEMPLATE/enrollment.yml, restoring the fields the
  [ENROLL] fast path in registration.yml parses (Full Name, Email
  Address, experience dropdowns, course goals) that were lost when
  classroom-enrollment.yml was deleted in the June 2 Classroom removal
- Point the REGISTER.md enrollment link at enrollment.yml
- Regenerate html/search-index.json

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: GitHub Workshop Bot

.github/ISSUE_TEMPLATE/bonus-a-improve-agent.yml

@@ -1,6 +1,5 @@
 name: "Bonus A: Improve an Existing Agent"
 description: Fork an agent, make a meaningful improvement, and open a PR.
-hidden: true
 title: "Bonus: Improve an Existing Agent (@{username})"
 labels: ["challenge", "bonus"]
 body:
@@ -37,7 +36,6 @@ body:
     attributes:
       label: "Your evidence"
       description: "Describe the agent you improved, what you changed, and link your PR."
-hidden: true
       placeholder: |
         Agent I improved: ...
         What I changed: ...

.github/ISSUE_TEMPLATE/bonus-b-document-journey.yml

@@ -1,6 +1,5 @@
 name: "Bonus B: Document Your Journey"
 description: Write a reflection document about your workshop experience.
-hidden: true
 title: "Bonus: Document Your Journey (@{username})"
 labels: ["challenge", "bonus"]
 body:
@@ -44,7 +43,6 @@ body:
     attributes:
       label: "Your evidence"
       description: "Share the link to your reflection file or PR."
-hidden: true
       placeholder: |
         Reflection URL: https://github.com/...
         My biggest takeaway: ...

.github/ISSUE_TEMPLATE/bonus-c-group-challenge.yml

@@ -1,6 +1,5 @@
 name: "Bonus C: Create a Group Challenge"
 description: Design a collaborative challenge for future workshop cohorts.
-hidden: true
 title: "Bonus: Create a Group Challenge (@{username})"
 labels: ["challenge", "bonus"]
 body:
@@ -40,7 +39,6 @@ body:
     attributes:
       label: "Your evidence"
       description: "Describe your group challenge and link to the file."
-hidden: true
       placeholder: |
         Challenge name: ...
         What teams would do: ...

.github/ISSUE_TEMPLATE/bonus-d-notifications.yml

@@ -1,6 +1,5 @@
 name: "Bonus D: Notification Mastery"
 description: Configure GitHub notifications for productive inbox management.
-hidden: true
 title: "Bonus: Notification Mastery (@{username})"
 labels: ["challenge", "bonus"]
 body:
@@ -37,7 +36,6 @@ body:
     attributes:
       label: "Your evidence"
       description: "Describe your notification configuration and strategy."
-hidden: true
       placeholder: |
         My notification strategy: ...
         I configured email for: ...

.github/ISSUE_TEMPLATE/bonus-e-git-history.yml

@@ -1,6 +1,5 @@
 name: "Bonus E: Explore Git History Visually"
 description: Use GitHub Desktop to explore repository history as a visual timeline.
-hidden: true
 title: "Bonus: Explore Git History Visually (@{username})"
 labels: ["challenge", "bonus"]
 body:
@@ -42,7 +41,6 @@ body:
     attributes:
       label: "Your evidence"
       description: "Describe what you discovered by exploring the Git history visually."
-hidden: true
       placeholder: |
         Tool I used: GitHub Desktop / GitHub.com
         Number of branches I found: ...

.github/ISSUE_TEMPLATE/challenge-01-find-your-way.yml

@@ -1,6 +1,5 @@
 name: "Challenge 1: Find Your Way Around"
 description: Navigate the learning-room repository and find key landmarks.
-hidden: true
 title: "Challenge 1: Find Your Way Around (@{username})"
 labels: ["challenge", "day-1"]
 body:
@@ -29,7 +28,6 @@ body:
     attributes:
       label: "Your evidence"
       description: "Paste your scavenger hunt findings below. For each item, write a short sentence about what you found."
-hidden: true
       placeholder: |
         1. I found ___ files in the root of the repository.
         2. The open issue I found was titled "___".

.github/ISSUE_TEMPLATE/challenge-03-conversation.yml

@@ -1,6 +1,5 @@
 name: "Challenge 3: Join the Conversation"
 description: Comment on a peer-simulation issue using @mentions and reactions.
-hidden: true
 title: "Challenge 3: Join the Conversation (@{username})"
 labels: ["challenge", "day-1"]
 body:
@@ -34,7 +33,6 @@ body:
     attributes:
       label: "Your evidence"
       description: "Paste the URL of the comment you left on the peer-simulation issue or buddy issue."
-hidden: true
       placeholder: |
         Comment URL: https://github.com/...
         I commented on the peer-simulation issue about...

.github/ISSUE_TEMPLATE/challenge-04-branch-out.yml

@@ -1,6 +1,5 @@
 name: "Challenge 4: Branch Out"
 description: Create your personal branch for Day 1 work.
-hidden: true
 title: "Challenge 4: Branch Out (@{username})"
 labels: ["challenge", "day-1"]
 body:
@@ -35,7 +34,6 @@ body:
     attributes:
       label: "Your evidence"
       description: "Confirm your branch name and describe how you created it."
-hidden: true
       placeholder: |
         My branch name: learn/myusername
         I created it by...

.github/ISSUE_TEMPLATE/challenge-05-make-your-mark.yml

@@ -1,6 +1,5 @@
 name: "Challenge 5: Make Your Mark"
 description: Edit welcome.md to fix a TODO and commit with a meaningful message.
-hidden: true
 title: "Challenge 5: Make Your Mark (@{username})"
 labels: ["challenge", "day-1"]
 body:
@@ -37,7 +36,6 @@ body:
     attributes:
       label: "Your evidence"
       description: "Paste the URL of your commit and share your commit message."
-hidden: true
       placeholder: |
         Commit URL: https://github.com/...
         My commit message was: "..."

.github/ISSUE_TEMPLATE/challenge-06-first-pr.yml

@@ -1,6 +1,5 @@
 name: "Challenge 6: Open Your First Pull Request"
 description: Open a PR from your branch to main, linking it to your issue.
-hidden: true
 title: "Challenge 6: Open Your First PR (@{username})"
 labels: ["challenge", "day-1"]
 body:
@@ -25,7 +24,6 @@ body:
         ### PR description template
 
         Use this structure for your PR description:
-hidden: true
 
         ```
         ## What this PR does
@@ -50,7 +48,6 @@ hidden: true
     attributes:
       label: "Your evidence"
       description: "Paste the URL of your pull request."
-hidden: true
       placeholder: |
         PR URL: https://github.com/...
         My PR links to issue #...