fix(agents): correct prompt hook docs, split modules, and fix install script

[illegalcall]

Summary

• Split rig-quality-gates module into rig-prompt-hooks (hook API docs) + rig-quality-gates (coding style & quality standards), fixing prompt hook content leaking into unrelated adapter files (e.g. vector-store)
• Fixed incorrect API references in AGENTS.md: CancelSignal::cancel() → ToolCallHookAction::Terminate/HookAction::Terminate, removed fictional dual-trait (PromptHook + StreamingPromptHook) section, added #[cfg] attributes to WasmCompat traits, expanded Capabilities example with Capable<T>/Nothing
• Fixed install-rig-skill.sh: install_gemini now appends instead of overwriting, SKILL_SOURCE detection no longer changes cwd
• Fixed grep pattern in rig-migrate skill and Self::NAME usage in tools.md
• Set executable bit (100755) on all three shell scripts — fixes CI "Permission denied" on sync_agent_instruction_files.sh
• Regenerated all 27 adapter files via sync script; validation passes

Test plan

• scripts/sync_agent_instruction_files.sh runs without errors
• scripts/validate_agent_instruction_files.sh confirms all adapters in sync
• Spot-check Claude Code skills (/rig-agent-scaffold, /rig-provider-checklist, /rig-review-gates)
• Verify install-rig-skill.sh --agent gemini appends correctly on a clean target

Fixes #1343

[joshua-mo-143]

Looks mostly OK, see comments

[joshua-mo-143]

Looks good to me. I think we will need to add some documentation on the docsite to match this.