chore: rename packages/ to crates/

Move all 29 workspace members from packages/<name>/ to crates/<name>/.
Updates: workspace Cargo.toml (members + path deps), justfile, root
CLAUDE.md, scripts/build/CARGO_INSTALL.md, docs/architecture/crates.md
(renamed from packages.md), structural references in docs/architecture
and docs/configuration, per-crate CLAUDE.md self-references. Historical
plans, reports, and building/ docs are left untouched.

No behavior change; just check-all stays green and fermata tests pass.

tests/fixtures/invalid_bad_timestamp.yaml

@@ -0,0 +1,17 @@
+version: "0.1"
+
+sessions:
+  - id: "session-1"
+    title: "Test Session"
+    created_at: "not-a-valid-date"
+    participants: []
+    messages: []
+
+responders:
+  keyword_map: {}
+  default_strategy: echo
+
+streaming:
+  enabled: false
+  tokens_per_chunk: 1
+  chunk_interval_ms: 100