docs: document every Maintainerr API endpoint

[enoch85]

Replaces the partial API page with complete reference documentation for all 219 Maintainerr endpoints.

What was added

Page	Endpoints	Covers
api/settings	74	Every integration's connection settings, connection tests, the media server switch
api/rules	29	Rule groups, execution, exclusions, community rules, YAML import and export
api/overlays	28	Overlay settings, processing runs, templates, fonts and images
api/collections	25	Collections, membership, bulk media actions, handling, posters, logs
api/media-server	23	Libraries, items, search, watch state, users, media server collections
api/notifications	8	Agents, configurations, rule group links, test sends
api/app-and-health	7	App status, time zone, releases, health probes, task status
api/logs	6	Log stream, log files, log level settings
api/seerr	6	Seerr lookups, requester names, request and media deletion
api/metadata-and-storage	6	Metadata provider lookups, storage metrics, the events stream
api/servarr	5	Radarr, Sonarr and Sportarr disk space and quality profiles
api/streamystats	2	Streamystats server info and per-item watch statistics

docs/API.md keeps its api id and /api slug and becomes a hub: the existing no-auth danger admonition, a new API conventions section, and a table of contents. The "does not yet embed the generated Swagger reference" note and the "Notable endpoints" framing are gone, since coverage is no longer partial.

Each endpoint has a summary, parameter table, request and response shapes, a status-code table with the real cause of each code, side effects, and the traps a caller would otherwise hit. All 46 destructive endpoints carry a warning saying what they destroy and whether it can be undone.

Conventions section

Cross-cutting facts that hold API-wide, so they are stated once rather than per endpoint: no authentication, no rate limiting, BASE_PATH, CORS, request validation (70 endpoints take a body, 17 with no schema), the OK/NOK envelope that reports failure inside a 200, POST answering 201, default error bodies, and which routes return secrets unmasked.

Bundled OpenAPI spec

static/openapi-spec/maintainerr_api_specs.yaml was badly stale and is regenerated from the current server.

	Before	After
Paths	120	187
Operations	152	239
Missing live paths	72	0
Paths that no longer exist	5	0

The 5 removed: /api/moviedb/image/{type}/{tmdbId}, /api/moviedb/movie/imdb/{id}, /api/moviedb/person/{personId}, /api/rules/exclusions/{plexId}, /api/rules/schedule/update.

The sidebars.js edit

AGENTS.md normally forbids touching sidebars. This PR edits it anyway, adding the twelve new ids under the existing API category. It is unavoidable: new doc pages have no route into the site otherwise, so without it the twelve pages would build but be unreachable. The edit is additive and changes nothing about the existing entries.

Scope

Only docs/, static/openapi-spec/ and that one sidebars.js line. versioned_docs/ is untouched.