feat(tags): Add database schema and tags module (v1.3.0 Phase 1)

Implements tag/category system backend following microformats2 p-category specification.

Database changes:
- Migration 008: Add tags and note_tags tables
- Normalized tag storage (case-insensitive lookup, display name preserved)
- Indexes for performance

New module:
- starpunk/tags.py: Tag management functions
  - normalize_tag: Normalize tag strings
  - get_or_create_tag: Get or create tag records
  - add_tags_to_note: Associate tags with notes (replaces existing)
  - get_note_tags: Retrieve note tags (alphabetically ordered)
  - get_tag_by_name: Lookup tag by normalized name
  - get_notes_by_tag: Get all notes with specific tag
  - parse_tag_input: Parse comma-separated tag input

Model updates:
- Note.tags property (lazy-loaded, prefer pre-loading in routes)
- Note.to_dict() add include_tags parameter

CRUD updates:
- create_note() accepts tags parameter
- update_note() accepts tags parameter (None = no change, [] = remove all)

Micropub integration:
- Pass tags to create_note() (tags already extracted by extract_tags())
- Return tags in q=source response

Per design doc: docs/design/v1.3.0/microformats-tags-design.md

Generated with Claude Code

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

migrations/008_add_tags.sql

@@ -0,0 +1,26 @@
+-- Migration 008: Add tag support for notes
+-- Version: 1.3.0
+-- Per microformats2 p-category specification
+
+-- Tags table (normalized tag storage)
+CREATE TABLE IF NOT EXISTS tags (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    name TEXT UNIQUE NOT NULL,           -- Normalized tag name (lowercase, trimmed)
+    display_name TEXT NOT NULL,          -- Original display name (preserves case)
+    created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+
+-- Note-tag junction table
+CREATE TABLE IF NOT EXISTS note_tags (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    note_id INTEGER NOT NULL,
+    tag_id INTEGER NOT NULL,
+    FOREIGN KEY (note_id) REFERENCES notes(id) ON DELETE CASCADE,
+    FOREIGN KEY (tag_id) REFERENCES tags(id) ON DELETE CASCADE,
+    UNIQUE(note_id, tag_id)
+);
+
+-- Indexes for performance
+CREATE INDEX IF NOT EXISTS idx_tags_name ON tags(name);
+CREATE INDEX IF NOT EXISTS idx_note_tags_note ON note_tags(note_id);
+CREATE INDEX IF NOT EXISTS idx_note_tags_tag ON note_tags(tag_id);