docs(readme): the README reflects the code it documents

[dbgeek]

What & why

A review of the README's Mermaid flowchart and Architecture section against src/ turned up drift, most of it from the 0.4.x releases. Two items were factually wrong rather than merely incomplete.

Corrected

• Vocabulary is no longer local-Whisper-only. The flowchart put "Vocabulary biases spelling" inside the local branch and the prose said it biases "local Whisper's spelling". Since Vocabulary biases OpenAI transcription at connect (keywords) #326/Vocabulary edits re-bind the warm session (rebias push) #327 the same shared list is bound as the OpenAI Session's keywords field on a keywords-capable model (session.zig) and re-bound on an idle push when the menu edits it (menu.zig). The flowchart now pins Vocabulary on the Backend Router and each backend node names how it applies it. The two stale config.zig comments that still called it local-only are fixed in the same pass — the vocabulary field doc, and the generated config.zon header line the daemon writes into the user's own config file.
• Secure Event Input was absent entirely, while the README claimed every Insertion leaves an Insertion Record. It does not: a positive probe on either Talk Key edge withholds that record from the ring and suppresses the transcript from the log even under .log_transcripts (Dictation under a held Secure Event Input is a decided, stated posture #286), and while SEI is held the chord never reaches the daemon at all (Surface a held Secure Event Input: the recovery chord silently never arrives #245). Now its own paragraph.
• Status line read v0.1.2 — six releases behind build.zig.zon.

Filled in

• api_key.zig, secure_input.zig, signing_identity.zig, broken_pipe.zig — missing from the module tables; the first three are named concepts in CONTEXT.md.
• vocabulary and log_transcripts — missing from a config table that opens with "Every field is optional".
• acceptance/ and tools/ in Repository Layout; --remove-model among the Model Operation subcommands.

Type of change

• Bug fix
• Documentation
• Small improvement
• Larger change (discussed first in issue #___)

Checklist

• Single, focused concern
• nix develop --command zig build test passes
• Uses the project vocabulary from CONTEXT.md
• Matches the surrounding code style

For the reviewer

Documentation only — no behavior change. The src/config.zig hunks are two comments; one of them is user-facing, since it is emitted into a freshly generated config.zon. No golden test pins that header, and the suite passes.

Verified against the code rather than assumed, and left alone because it already matched: the Coordinator's five phases, the Insert Worker's dictation → menu → Undo drain order, the ring's N=20, all ten pre-existing config defaults, the key precedence, and every build step and link the README names.

One thing deliberately not touched: docs/vocab-biasing-spec.md still states the local-only rule in three places. It is a locked spec whose successor docs/openai-biasing-spec.md already records that premise as superseded, so amending it looked like it would work against the convention rather than with it. Happy to change that if you'd rather the old spec carry a pointer.