…nted client filter values

Charm Crush is a recognized aibridge.Client constant, but we have no
client config page or compatibility-table entry for it. Listing it here
without a companion config page is misleading: users would learn the
filter value exists but have no way to set up the client to begin with.

Removing it from the documented filter list keeps the doc aligned with
configurable client coverage. The constant remains in
aibridge/client.go and the SQL filter still accepts the literal string
if a caller already knows it.

Generated by Coder Agents on behalf of David Fraley.

… Compatible guidance

Reflect what AI Gateway actually does for Coder Agents traffic and
fix inaccurate guidance in the configuration tabs.

- Authentication: AI Gateway resolves the bearer token to a Coder user
  and uses that user (not the chat owner) as the initiator. Strongly
  recommend a service-account token instead of an admin token.
- Identity headers: only User-Agent and X-Coder-Chat-Id are consumed
  by AI Gateway today. Note that X-Coder-Owner-Id, X-Coder-Subchat-Id,
  and X-Coder-Workspace-Id are emitted but not yet read.
- OpenAI Compatible: drop the misleading multi-instance Anthropic
  example. OpenAI Compatible speaks the OpenAI wire protocol, so it
  cannot target Anthropic-typed instances. Document its actual use
  case (opting out of OpenAI-specific options on a named OpenAI-typed
  instance) and add inline guidance under the OpenAI and Anthropic
  tabs for targeting named instances via the matching provider type.
- Verifying the integration: the initiator shown is the API token's
  user, not the chat owner.
- Add a Known limitations section covering the attribution gap and
  BYOK exclusion.

Generated by Coder Agents on behalf of David Fraley.

…o a single procedure

The Anthropic, OpenAI, and OpenAI Compatible tabs all walked through the
same six-step procedure with only the Base URL differing. Replace the
three tabs with one procedure and a Base URL reference table.

Move the OpenAI Compatible 'when to use' guidance into its own subsection
linked from the table, since it's the one provider type that needs extra
context (it speaks the OpenAI wire protocol regardless of the upstream
provider on AI Gateway).

Generated by Coder Agents on behalf of David Fraley.

…bution wording and clarify provider scope

- Tighten the 'Identity and correlation headers' section so it explicitly
  ties X-Coder-Owner-Id (and the other unconsumed Coder headers) to the
  attribution gap and links to Known limitations. The behavior was
  already accurate; this just makes the cause/effect chain explicit.
- Drop the broken anchor link in the Configuration table
  (#when-to-use-openai-compatible was removed in a prior commit).
- Add a note that the documented provider examples (Anthropic, OpenAI,
  OpenAI Compatible) are not exhaustive. Coder Agents also supports
  Azure OpenAI, AWS Bedrock, Google, OpenRouter, and Vercel AI Gateway
  provider types, but routing through AI Gateway is bounded by the wire
  protocols AI Gateway speaks (Anthropic, OpenAI, Copilot today).

Generated by Coder Agents on behalf of David Fraley.