v5.0.3 - Pinned items + schema hardening

Pinned items (GUI feature integration) and schema hardening.

Added

• New CLI command cm pinned - read-only listing of items curated in
  the optional GUI (context-wolf-ui). Output as grouped Markdown, with
  --project filter and --json output. Returns empty silently when
  GUI tables are missing.
• New optional MCP tool pinned_list - conditionally registered at
  server startup. Only appears in the tool schema when the pinned_items
  table exists (i.e., when the GUI is installed). Keeps the MCP schema
  lean for CLI-only installations.
• Migration 003: pinned_item_projects table for many-to-many project
  scopes on pinned items (an item with no scope rows is global).
• Migration 005: CHECK constraints on ai_instructions.scope and
  priority columns to enforce the canonical vocabulary at the DB level.

Changed

• Renamed feature "Promptstart" to "Pinned" across schema, GUI, CLI,
  MCP tool, and docs. The old name collided semantically with cm ai-prompt
  (different feature: auto session-starter vs. curated items). Fresh
  installs use the new naming; existing installations can upgrade via
  ALTER TABLE (manual, no downtime, no data loss).
• Migration 002 renamed: promptstart_items -> pinned_items with
  corresponding index renames.
• All cm init flows updated to reflect the new naming.

Fixed

• Migration 004: normalized ai_instructions.priority = 'may' rows to
  'nice' (CLI vocabulary), cleaning up drift from an earlier GUI
  implementation that used the RFC 2119 term.