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

tests/fixtures/invalid_bad_yaml.yaml

@@ -0,0 +1,5 @@
+version: "0.1"
+sessions:
+  - id: "session-1
+    title: "Unclosed quote
+    this is not valid yaml: [broken

tests/fixtures/invalid_duplicate_session.yaml

@@ -0,0 +1,22 @@
+version: "0.1"
+
+sessions:
+  - id: "session-1"
+    title: "First Session"
+    created_at: "2024-01-01T00:00:00Z"
+    participants: []
+    messages: []
+  - id: "session-1"
+    title: "Duplicate Session"
+    created_at: "2024-01-01T00:00:00Z"
+    participants: []
+    messages: []
+
+responders:
+  keyword_map: {}
+  default_strategy: echo
+
+streaming:
+  enabled: false
+  tokens_per_chunk: 1
+  chunk_interval_ms: 100

tests/fixtures/invalid_version.yaml

@@ -0,0 +1,17 @@
+version: "0.2"
+
+sessions:
+  - id: "session-1"
+    title: "Test Session"
+    created_at: "2024-01-01T00:00:00Z"
+    participants: []
+    messages: []
+
+responders:
+  keyword_map: {}
+  default_strategy: echo
+
+streaming:
+  enabled: false
+  tokens_per_chunk: 1
+  chunk_interval_ms: 100

tests/fixtures/valid_basic.yaml

@@ -0,0 +1,37 @@
+version: "0.1"
+
+sessions:
+  - id: "session-1"
+    title: "Basic Test Session"
+    created_at: "2024-01-01T00:00:00Z"
+    participants:
+      - id: "user-1"
+        kind: user
+        display_name: "Test User"
+      - id: "assistant-1"
+        kind: assistant
+        display_name: "Test Assistant"
+    messages:
+      - id: "msg-1"
+        session_id: "session-1"
+        role: user
+        content: "Hello, assistant!"
+        created_at: "2024-01-01T00:00:01Z"
+      - id: "msg-2"
+        session_id: "session-1"
+        role: assistant
+        content: "Hello! How can I help you today?"
+        created_at: "2024-01-01T00:00:02Z"
+        parent_id: "msg-1"
+
+responders:
+  keyword_map:
+    hello: "Hi there!"
+    help: "I can assist you with various tasks."
+  default_strategy: echo
+
+streaming:
+  enabled: true
+  tokens_per_chunk: 5
+  chunk_interval_ms: 100
+  jitter_ms: 20

tests/fixtures/valid_complex.yaml

@@ -0,0 +1,82 @@
+version: "0.1"
+
+sessions:
+  - id: "session-chat"
+    title: "Complex Chat Session"
+    created_at: "2024-01-01T10:00:00Z"
+    participants:
+      - id: "user-1"
+        kind: user
+        display_name: "Alice"
+      - id: "assistant-1"
+        kind: assistant
+        display_name: "Bob AI"
+      - id: "system-1"
+        kind: system
+    messages:
+      - id: "msg-1"
+        session_id: "session-chat"
+        role: system
+        content: "System initialized"
+        created_at: "2024-01-01T10:00:00Z"
+      - id: "msg-2"
+        session_id: "session-chat"
+        role: user
+        content: "What's the weather?"
+        created_at: "2024-01-01T10:00:05Z"
+        parent_id: "msg-1"
+      - id: "msg-3"
+        session_id: "session-chat"
+        role: assistant
+        content: "Let me check that for you."
+        created_at: "2024-01-01T10:00:06Z"
+        parent_id: "msg-2"
+        metadata:
+          thinking: true
+          confidence: 0.95
+      - id: "msg-4"
+        session_id: "session-chat"
+        role: assistant
+        content: "The weather is sunny with a temperature of 72°F."
+        created_at: "2024-01-01T10:00:08Z"
+        parent_id: "msg-3"
+
+  - id: "session-debug"
+    title: "Debug Session"
+    created_at: "2024-01-02T00:00:00Z"
+    participants:
+      - id: "dev-1"
+        kind: user
+        display_name: "Developer"
+      - id: "tool-1"
+        kind: tool
+        display_name: "Debugger"
+    messages:
+      - id: "debug-1"
+        session_id: "session-debug"
+        role: user
+        content: "Run diagnostic"
+        created_at: "2024-01-02T00:00:01Z"
+    behavior:
+      responder: fixture_only
+      streaming:
+        enabled: false
+        tokens_per_chunk: 1
+        chunk_interval_ms: 50
+
+responders:
+  keyword_map:
+    weather: "The weather is sunny."
+    time: "The current time is noon."
+  default_strategy: keywords
+  random:
+    seed: 42
+    corpus:
+      - "Random response 1"
+      - "Random response 2"
+      - "Random response 3"
+
+streaming:
+  enabled: true
+  tokens_per_chunk: 10
+  chunk_interval_ms: 50