feat: add voice-mode plugin with /voice command

[anmolp1]

Summary

Adds a voice-mode plugin with a /voice command so the startup banner instruction actually works for plugin-enabled users.

The startup banner says ✻ Voice mode is now available · /voice to enable, but on some versions this returns "Unknown skill: voice". This plugin bridges that gap by providing a /voice command that manages voiceEnabled in ~/.claude/settings.local.json.

Closes #33914

What's included

• plugins/voice-mode/commands/voice.md — Slash command supporting /voice, /voice on, /voice off, and /voice status
• plugins/voice-mode/.claude-plugin/plugin.json — Plugin manifest
• Marketplace registration — Added to .claude-plugin/marketplace.json under the accessibility category

Design decisions

• Writes to settings.local.json (not settings.json) to respect the user-local / version-controlled split
• Preserves existing settings via jq merge ('. + {"voiceEnabled": true}'), never overwrites the file
• Falls back gracefully if jq is unavailable — provides manual instructions instead of failing
• Uses model: haiku since the operation is simple (read JSON, toggle a boolean, write JSON)

Note on built-in /voice

Recent Claude Code versions (tested on v2.1.74) appear to have a built-in /voice command that writes to settings.json. This plugin serves as:

• A fallback for versions where /voice is not yet recognized
• A reference implementation showing how settings-toggling commands can be packaged as plugins
• A discoverable workaround users can install today via /plugin install voice-mode

Test plan

• Plugin JSON and marketplace JSON are valid
• Command frontmatter parses correctly (description, allowed-tools, model)
• Enable: jq '. + {"voiceEnabled": true}' sets the flag without dropping existing keys
• Disable: jq '. + {"voiceEnabled": false}' sets the flag without dropping existing keys
• Idempotent: enabling when already enabled is a no-op
• Full toggle cycle preserves all original settings keys
• Creating settings.local.json from scratch produces valid JSON
• Marketplace entry points to a valid source directory
• End-to-end: /plugin install voice-mode → /voice enables voice mode (requires interactive session)

Validation results

#	Test	Result
1	Status check reads voiceEnabled	PASS
2	Enable sets voiceEnabled: true	PASS
3	Existing settings preserved after enable	PASS
4	Idempotent enable (no-op when already on)	PASS
5	Disable sets voiceEnabled: false	PASS
6	Re-enable after disable	PASS
7	All original keys survive full toggle cycle	PASS
8	Create settings file from scratch	PASS
9	Command frontmatter valid	PASS
10	Marketplace entry valid and path exists	PASS

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