fix(plugin-dev): document repository as string-only in manifest docs

[Codeturion]

Summary

plugins/plugin-dev/skills/plugin-structure/references/manifest-reference.md documents the repository field as accepting both string and object formats. The runtime schema only accepts a string; passing an object fails install with repository: Invalid input: expected string, received object. The same file (and examples/advanced-plugin.md) also use the wrong object form in two complete-example blocks. Update the field docs to string-only and rewrite both examples to match.

Files changed

• plugins/plugin-dev/skills/plugin-structure/references/manifest-reference.md (field docs at the #### repository section, plus the full-config example near the end)
• plugins/plugin-dev/skills/plugin-structure/examples/advanced-plugin.md (full-config example)

Verification

Setup. Static check that no object-form repository JSON remains in the plugins/plugin-dev/ tree, and that all pre-existing string-form repository instances are unchanged. Compares the upstream main version of the two affected files against the patched versions on this branch using git show main:<path>.

Details. Run from the fork root: bash notes/repro-43722/verify.sh (the script is included as a reproduction artifact in the working notes, not in this PR). The check is grep -rnE '"repository":[[:space:]]*\{' plugins/plugin-dev for object form, and grep -rnE '"repository":[[:space:]]*"https' plugins/plugin-dev for string form. The runtime install failure was not reproduced in a live harness; the schema mismatch is documented in the issue body and is the canonical justification for the fix.

Comparisons.

Location	Pre-fix	Post-fix
manifest-reference.md #### repository (line ~150)	object form documented as supported	section says String (URL) only, with explicit "object form is not supported" callout
manifest-reference.md full-config example (line ~498)	object form	string form
advanced-plugin.md full-config example (line ~116)	object form	string form
manifest-reference.md line 142 (string-form example)	string	string (unchanged)
manifest-reference.md line 467 (string-form example)	string	string (unchanged)
examples/standard-plugin.md line 51	string	string (unchanged)
plugin-structure/SKILL.md line 77	string	string (unchanged)

Pre-fix object-form instances: 3. Post-fix: 0. String-form instances unchanged: 4.

Regression. No previously-correct example was modified. The only content removed is the "Object format (detailed)" subsection and the two object-form example blocks; both replaced with the single supported string form.

Refs

Fixes #43722

[Codeturion]

Wider regression check

Beyond the per-instance object-form check in the PR body, ran a repo-wide sweep for anything that depends on the documented (incorrect) object-form repository:

• Validator agents. plugins/plugin-dev/agents/plugin-validator.md does not check the repository field at all (no repository mention in the file). No agent or skill validates the object form.
• Other docs / examples. Zero occurrences of object-form "repository": { anywhere outside the three locations this PR fixes. All four other repository references in the plugin-dev tree (standard-plugin.md, two further string-form examples in manifest-reference.md, and plugin-structure/SKILL.md) already use the correct string form.
• Workflows / CI / tests. No workflow, script, or test file references either form. CHANGELOG does not document the object form.

No additional files needed changes; the inconsistency the issue cites was localized to exactly these three locations.