VS Code extension: add 12 missing chat participant commands

[bilersan]

Summary

The VS Code extension currently supports 16 chat participant commands. Many ctx CLI subcommands added since v0.3.0 have no corresponding chat participant coverage, requiring users to switch to the terminal.

Missing Commands

The following ctx commands have no chat participant handler:

Command	Purpose
changes	Show what changed since last session
config	Manage runtime configuration profiles
doctor	Structural health check
guide	Quick-reference cheat sheet
why	Read the philosophy behind ctx
memory	Bridge Claude Code auto memory into .context/
prompt	Manage reusable prompt templates
decisions	Manage DECISIONS.md file
learnings	Manage LEARNINGS.md file
deps	Show package dependency graph
journal	Analyze exported AI sessions
reindex	Regenerate indices for DECISIONS.md and LEARNINGS.md

Additional Issues

• No activation event for chat participant (lazy activation may miss early invocations)
• No splitArgs helper — commands with quoted arguments don't parse correctly
• Missing Apache-2.0 LICENSE file for the extension package
• Test coverage is 53 tests for 16 commands; new commands need matching tests
• execFile calls don't use shell: true on Windows, so PATH resolution fails for executables without .exe extension

Proposed Fix

• Add 12 new handler functions with full subcommand routing
• Add splitArgs helper for quoted argument parsing
• Add onChatParticipant:ctx.participant activation event
• Add Apache-2.0 LICENSE file
• Add 78 new tests (53 → 131 total)
• Enable Windows shell mode in execFile for cross-platform PATH resolution

[bilersan]

Superseded by PR #36 which delivers the full VS Code extension with all 45 slash commands (including the 12 missing ones tracked here).