v0.3.0: rename app Daybook -> AgentFeed

Removes the "Daybook" name from everything user- and agent-facing, since no
agents are configured yet and this is the cheap moment to do it.

- UI brand, docs, README, CLAUDE.md -> AgentFeed.
- Ingest env vars DAYBOOK_URL/TOKEN/SOURCE/DATA_DIR/BIND_ADDR/HOST_DATA_DIR/
  KEY_PROVISIONING_API -> AGENTFEED_* (token *values* unchanged).
- Skill: skills/daybook-posting -> skills/agentfeed-posting, daybook_post.py
  -> agentfeed_post.py (+ scripts/ wrapper and its test).
- static/daybook.css -> static/agentfeed.css; localStorage daybook.* ->
  agentfeed.*; templatetag daybook_extras -> agentfeed_extras; multipart
  boundaries; json/csv viewer element ids; daybook_exception_handler ->
  agentfeed_exception_handler; compose service/container -> agentfeed.
- Key-provisioning API now OFF by default (independent of DEBUG); enable with
  AGENTFEED_KEY_PROVISIONING_API=1 on test installs only.
- Posting helper now points at Settings -> API Keys.

Deferred on purpose (a later, separate step): the Django package
`daybook_project`, the `/opt/daybook` install path, and the Forgejo repo name.
The sibling AGENT_DAYBOOK__LLM_TEST name is intentionally untouched.

Full suite: 129 passing; live server verified serving under the new name.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

deploy/docker-compose.yml

@@ -1,4 +1,4 @@
-# ${VAR} substitution below (DAYBOOK_BIND_ADDR, DAYBOOK_HOST_DATA_DIR) reads
+# ${VAR} substitution below (AGENTFEED_BIND_ADDR, AGENTFEED_HOST_DATA_DIR) reads
 # from deploy/.env because Compose resolves .env relative to *this file's*
 # directory, not the caller's cwd. That relies on being invoked as
 # `docker compose -f deploy/docker-compose.yml` from the repo root, per
@@ -7,20 +7,20 @@
 # the defaults (0.0.0.0 bind, ./data) would be a security regression, not
 # just a broken build.
 services:
-  daybook:
+  agentfeed:
     build:
       context: ..
       dockerfile: deploy/Dockerfile
-    container_name: daybook
+    container_name: agentfeed
     restart: unless-stopped
     env_file:
       - .env
     mem_limit: 384m
     mem_reservation: 128m
     ports:
-      - "${DAYBOOK_BIND_ADDR:-0.0.0.0}:8000:8000"
+      - "${AGENTFEED_BIND_ADDR:-0.0.0.0}:8000:8000"
     volumes:
-      - ${DAYBOOK_HOST_DATA_DIR:-./data}:/data
+      - ${AGENTFEED_HOST_DATA_DIR:-./data}:/data
     healthcheck:
       # Hit the login page, not /api/capabilities: capabilities returns 403
       # when unauthenticated, and `curl --fail` treats 403 as an error, which