feat(memory): enable temporal decay with access-recency boost

The holographic retriever had temporal decay implemented but disabled
(half_life=0). All facts scored equally regardless of age — a 2-year-old
fact about a deprecated tool scored the same as yesterday's deployment
config.

This commit:
1. Changes default temporal_decay_half_life from 0 to 60 days
   - 60 days: facts lose half their relevance every 2 months
   - Configurable via config.yaml: plugins.hermes-memory-store.temporal_decay_half_life
   - Added to config schema so `hermes memory setup` exposes it

2. Adds access-recency boost to search scoring
   - Facts accessed within 1 half-life get up to 1.5x boost on their decay factor
   - Boost tapers linearly from 1.5 (just accessed) to 1.0 (1 half-life ago)
   - Capped at 1.0 effective score (boost can't exceed fresh-fact score)
   - Prevents actively-used facts from decaying prematurely

3. Scoring pipeline: score = relevance * trust * decay * min(1.0, access_boost)
   - Fresh facts: decay=1.0, boost≈1.5 → score unchanged
   - 60-day-old, recently accessed: decay=0.5, boost≈1.25 → score=0.625
   - 60-day-old, not accessed: decay=0.5, boost=1.0 → score=0.5
   - 120-day-old, not accessed: decay=0.25, boost=1.0 → score=0.25

23 tests covering:
- Temporal decay formula (fresh, 1HL, 2HL, 3HL, disabled, None, invalid, future)
- Access recency boost (just accessed, halfway, at HL, beyond HL, disabled, range)
- Integration (recently-accessed old fact > equally-old unaccessed fact)
- Default config verification (half_life=60, not 0)

Fixes #241

plugins/memory/holographic/__init__.py

@@ -12,7 +12,7 @@ Config in $HERMES_HOME/config.yaml (profile-scoped):
       auto_extract: false
       default_trust: 0.5
       min_trust_threshold: 0.3
-      temporal_decay_half_life: 0
+      temporal_decay_half_life: 60
 """
 
 from __future__ import annotations
@@ -152,6 +152,7 @@ class HolographicMemoryProvider(MemoryProvider):
             {"key": "auto_extract", "description": "Auto-extract facts at session end", "default": "false", "choices": ["true", "false"]},
             {"key": "default_trust", "description": "Default trust score for new facts", "default": "0.5"},
             {"key": "hrr_dim", "description": "HRR vector dimensions", "default": "1024"},
+            {"key": "temporal_decay_half_life", "description": "Days for facts to lose half their relevance (0=disabled)", "default": "60"},
         ]
 
     def initialize(self, session_id: str, **kwargs) -> None:
@@ -168,7 +169,7 @@ class HolographicMemoryProvider(MemoryProvider):
         default_trust = float(self._config.get("default_trust", 0.5))
         hrr_dim = int(self._config.get("hrr_dim", 1024))
         hrr_weight = float(self._config.get("hrr_weight", 0.3))
-        temporal_decay = int(self._config.get("temporal_decay_half_life", 0))
+        temporal_decay = int(self._config.get("temporal_decay_half_life", 60))
 
         self._store = MemoryStore(db_path=db_path, default_trust=default_trust, hrr_dim=hrr_dim)
         self._retriever = FactRetriever(