docs: add Poll Lane and Sighting to the shared vocabulary (#104)

Two new glossary terms in `CONTEXT.md`, settled in a design session, plus the graphify refresh.

- **Poll Lane** — one Site's own stream of Polls, carrying the pace at which that Site is willing to be asked. No Lane can slow, block or borrow from another's; a Reader never has one.
- **Sighting** — what a Reader's browser happened to see of a Series's Latest Chapter. Reports the same fact as a Poll, carries none of its authority.
- **Latest Chapter** amended: it no longer claims to be discovered without the reader present, since a Sighting establishes it between Polls.

No code. The work these terms describe is specified in #98 (comix), #101 (Poll Lanes), #102 (admin page) and #103 (Sightings).

Reviewed-on: #104
Co-authored-by: Sulthan Zaki <sultankiki05@gmail.com>
Co-committed-by: Sulthan Zaki <sultankiki05@gmail.com>

graphify-out/.graphify_labels.json

@@ -15,6 +15,7 @@
   "13": "Web UI Handlers",
   "14": "Go Error Handling",
   "15": "CDP Browser Client",
+  "16": "Cloudflare bot scoring and poll cadence — what is actually documented",
   "17": "Go Code Style Guide",
   "18": "Agent Skills",
   "20": "I/O Performance Patterns",
@@ -23,7 +24,6 @@
   "23": "Browser Entrypoint",
   "24": "Memory Allocation & GC",
   "25": "Cover Fetcher Tests",
-  "26": "readSeries",
   "27": "Find Skills Guide",
   "28": "Allocation Patterns",
   "29": "Observability & Alerting",