feat(governance): add typed label and governance outputs

[SamMorrowDrums]

Summary

Add concrete output types and schemas for all label tools, repository rulesets, and custom properties. Structured content is exposed only to the supported modern protocol; legacy text output, error behavior, level/method routing, scopes, and IFC metadata remain compatible.

Why

Continue the sequential typed-output stack on top of the Projects layer. Builds on #3401; no issue linked.

What changed

• Typed both get_label registrations, list_label, label_write, repository_ruleset_read, create_repository_ruleset, and custom properties read/write.
• Added protocol-gated wire tests for modern, legacy, empty, and unknown protocol versions, plus typed snapshots and regenerated documentation.

MCP impact

• No tool or API changes
• Tool schema or behavior changed — adds concrete output schemas and modern structured content while preserving legacy text responses.
• New tool added

Prompts tested (tool changes only)

• No natural-language prompts; direct MCP wire tests exercised label reads/writes, custom-property reads/writes at each level, and ruleset reads/writes across supported methods.

Security / limits

• No security or limits impact
• Auth / permissions considered — existing level-specific scope challenges are preserved.
• Data exposure, filtering, or token/size limits considered — response fields remain faithful; no authorization or limit behavior changed.

Tool renaming

• I am renaming tools as part of this PR (e.g. a part of a consolidation effort)
  • I have added the new tool aliases in deprecated_tool_aliases.go
• I am not renaming tools as part of this PR

Note: if you're renaming tools, you must add the tool aliases. For more information on how to do so, please refer to the official docs.

Lint & tests

• Linted locally with ./script/lint (invoked as script/lint; passed with 0 issues).
• Tested locally with ./script/test (invoked as script/test; passed, including go test -race ./...).

Validation in order: UPDATE_TOOLSNAPS=true go test ./... — passed; script/lint — passed (0 issues); script/test — passed; script/generate-docs — passed and updated generated docs; git diff --check — passed.

Docs

• Not needed
• Updated (README / docs / examples) — regenerated README tool documentation.