Add mkdocs-llmstxt plugin and remove hand-written llms.txt

[gregology]

Why

The current hand-written llms.txt links to rendered HTML pages on sctx.dev, so agents pulling those URLs get the full MkDocs Material chrome — nav, scripts, theme markup. Not useful for consumption. There's also no llms-full.txt, which is what most agents look for as a single-file dump of all docs.

What this does

Swaps the hand-written docs/llms.txt for the mkdocs-llmstxt plugin, which auto-generates both llms.txt and llms-full.txt at build time. The generated llms.txt links to .md versions of pages instead of HTML, and llms-full.txt concatenates all doc content into one file (~1000 lines).

The plugin is configured with explicit sections that mirror the structure from the old hand-written file, and the markdown_description carries over the same introductory paragraph.

The old docs/llms.txt source file is deleted because it would conflict with the plugin's output (both try to produce llms.txt in the build).

Alternatives considered

Build script (concat): A simple shell script or Makefile target that cats the markdown files together. No new deps, full control. Downside: nav order has to be kept in sync manually with mkdocs.yml. With only 8 doc pages this is fine today, but the plugin approach follows an existing convention and stays in sync automatically. Greg preferred this reasoning.

Raw markdown serving: Copy .md files into the build output so agents can fetch individual pages as clean markdown. More flexible but more moving parts in the deploy pipeline, and could confuse human visitors landing on raw markdown URLs. Overkill for now.

Review walkthrough

Single commit covering one coherent change (splitting it would leave a broken intermediate state):

• Add mkdocs-llmstxt plugin and remove hand-written llms.txt — Adds mkdocs-llmstxt==0.5.0 to docs/requirements.txt, configures the llmstxt plugin in docs/mkdocs.yml with sections/descriptions/full_output, explicitly lists search plugin (adding a plugins: key overrides MkDocs defaults), and deletes docs/llms.txt.

Closes #116

Developer metrics

Total duration: 7m 30s
Turns: 129
Tool calls: 108
Tokens: 1,501,005 input / 10,473 output

Stage	Model	Duration	Turns	Tool calls	Tokens (in/out)	Cache read	Cache creation
triage	claude-opus-4-6	1m 29s	41	38	84,806 / 1,227	70,115	14,684
decompose	claude-opus-4-6	2m 25s	28	25	702,742 / 4,129	675,313	27,399
implement_step_1	claude-opus-4-6	1m 52s	29	21	229,759 / 2,588	212,606	17,134
docs_review	claude-opus-4-6	0m 22s	10	7	139,311 / 721	117,938	21,363
craft_pr	claude-opus-4-6	1m 20s	21	17	344,387 / 1,808	306,826	37,543

Resolves #116

[gregology]

should full_output: llms-full.txt be full_output: llms.txt? Is there a good reason to use llms-full.txt?

[gregology]

Reviewed the feedback -- nothing actionable to address programmatically.

Developer metrics

Total duration: 0m 49s
Turns: 13
Tool calls: 9
Tokens: 81,997 input / 1,200 output

Stage	Model	Duration	Turns	Tool calls	Tokens (in/out)	Cache read	Cache creation
analyze_feedback	claude-opus-4-6	0m 41s	12	9	59,574 / 1,025	44,955	14,615
no_action_comment	claude-opus-4-6	0m 7s	1	0	22,423 / 175	8,545	13,876