feat: claude-supermemory parity - entity context, dedup, relative time, repo tag, signal extraction

Ports all major features from claude-supermemory to opencode-supermemory-max:

1. Entity Context: PERSONAL_ENTITY_CONTEXT and REPO_ENTITY_CONTEXT
   constants guide supermemory on what to extract from conversations
   (user intent, decisions, preferences vs architecture, patterns)

2. Dedup: deduplicate search results and profile facts to avoid
   showing the same memory multiple times

3. Relative Time: show '3hrs ago', '2d ago' etc. alongside similarity
   percentages for memory results with timestamps

4. Repo Container Tag: 3-tier memory scopes (user/project/repo)
   - repo tag based on git remote name for team-shared knowledge
   - search, add, list all support scope='repo'
   - session-end saves to all 3 scopes

5. Signal Extraction: importance-based filtering for session saves
   - only saves turns containing signal keywords (configurable)
   - includes N context turns before each signal for continuity
   - English + Japanese signal keywords built-in
   - disabled by default (set signalExtraction: true to enable)