P3: meta + primitive tool group (think/now/cite + classify/extract/summarize)

Grow executus/tools into a real generic tool library:

- Register(reg): the always-available, zero-config tools — think, now (UTC
  unless a CurrentTimeProvider is wired), cite (inert unless a CitationStorage
  is wired). All nil-safe; a light host calls Register and is useful.
- RegisterMeta(reg, MetaDeps): the LLM-backed meta tools — classify,
  extract_entities, summarize — over the llmmeta helper. Budget defaults to the
  shipped in-memory per-run cap; Files optional; caps default.
- Seams moved (interface/type-only, no host coupling): research_providers.go
  (CurrentTimeProvider/CitationStorage/SearchBudget/PageExtractor/PDFFetcher/…)
  and file_storage.go (FileStorage + FileDomainMeta). Plus the in-memory budget
  default (research_defaults.go) and scope_validate.go.

calculate deferred (drags github.com/Krognol/go-wolfram + a module-path replace
— not worth it in the lean core for one tool). Core go.sum still free of
gorm/redis/discordgo/sqlite/wolfram.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -58,11 +58,13 @@ CORE (majordomo + stdlib):
              structured output — no separate structured/ pkg)
   llmmeta/  shared meta-LLM helper over model/            [P1 ✓]
   compact/  context compactor (WithCompactor hook)       [P2 ✓]
-  tools/    generic tool library + Register entrypoint;  [P3 wip]
-            think moved; end-to-end "agent calls a tool"
-            test green. Remaining: meta/web/net/store/
-            compose groups + their nil-safe Deps + default
-            backends (the default.go grab-bag split)      [P3]
+  tools/    generic tool library: Register (think/now/    [P3 wip]
+            cite, zero-config) + RegisterMeta (classify/
+            extract_entities/summarize); seams in
+            research_providers.go/file_storage.go;
+            in-memory budget default. End-to-end "agent
+            calls a tool" test green. Remaining: web/net/
+            store/compose groups + their backends         [P3]
 
 BATTERIES (opt-in siblings, each nil-safe + a default):
   persona/   Agent noun + AgentStore seam + yml loader   [P4]