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>

hooks/hooks.json

@@ -1,5 +1,16 @@
 {
   "hooks": {
+    "UserPromptSubmit": [
+      {
+        "hooks": [
+          {
+            "type": "command",
+            "command": "~/.claude/hooks/scripts/prompt-context.py",
+            "timeout": 5
+          }
+        ]
+      }
+    ],
     "SessionStart": [
       {
         "hooks": [