feat(ttp): E.1.11 RuleStore contract — base ABC, factory, filesystem + database stubs

Adds decnet/ttp/store/ subpackage:
- base.py: RuleState frozen dataclass, RuleChange NamedTuple, RuleStore ABC
- factory.py: get_rule_store() reading DECNET_TTP_RULE_STORE_TYPE
- impl/filesystem.py: FilesystemRuleStore with sys.platform=='linux'
  fail-fast guard, allowlist filename regex, raw inotify mask bits
  (lib import deferred to E.3 so contract phase compiles without the
  asyncinotify dep installed)
- impl/database.py: DatabaseRuleStore stub (no platform guard)

TTPRule + TTPRuleState SQLModels were already shipped at E.1.1; this
commit closes the type-only TYPE_CHECKING forward-ref in
rule_engine.py via real runtime imports through the new package.

development/TTP_TAGGING.md

@@ -2374,6 +2374,8 @@ unrelated events.
 **E.1.11 — RuleStore contract**
 (`decnet/ttp/store/{base.py, factory.py, impl/}`)
 
+**Status:** ✅ done.
+
 - `class RuleState` frozen dataclass: state literal
   ("enabled" | "disabled" | "clipped"), `confidence_max`,
   `expires_at`, `reason`, `set_by`, `set_at`. Default constructor