Add UserPromptSubmit hook for context injection

Injects contextual information when user submits a prompt:
- Current time with period (morning/afternoon/evening/night)
- Git branch if in a repository
- Relevant memory items based on prompt keywords (2+ matches)
- Pending decisions needing attention

Design:
- Skips short prompts (<10 chars) to not slow down commands
- 5s timeout to keep prompts responsive
- Lightweight keyword matching for memory relevance

Also updates general-instructions.json with git workflow notes.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

state/personal-assistant/general-instructions.json

@@ -7,6 +7,18 @@
       "instruction": "Delegate technical tasks to specialized agents. Use skills and slash commands for quick technical checks.",
       "status": "active",
       "added": "2025-01-21"
+    },
+    {
+      "id": "b2c3d4e5-6789-01bc-def0-222222222222",
+      "instruction": "Create a new git branch when working on new features (e.g., feature/descriptive-name). Commit work to the branch before rebasing and pushing.",
+      "status": "active",
+      "added": "2026-01-03"
+    },
+    {
+      "id": "c3d4e5f6-7890-12cd-ef01-333333333333",
+      "instruction": "The ~/.claude repo uses Gitea (not GitHub). After pushing a branch, create PR manually via Gitea web UI - gh CLI won't work.",
+      "status": "active",
+      "added": "2026-01-03"
     }
   ]
 }