fix(catalog): rename the DeepSeek flash model to its canonical id deepseek-flash

[argszero]

Summary

Rename the DeepSeek flash model to its current canonical id deepseek-flash.

The upstream docs (https://api-docs.deepseek.com/zh-cn/ , checked 2026-09-14) now name the model
deepseek-flash; deepseek-v4-flash and deepseek-v4-flash-vision-exp are retired (requests to
those names still answer, but DeepSeek routes them to DeepSeek-V4.1-Flash and bills Flash prices).
deepseek-v4-pro is unchanged.

Why it mattered: POST /api/sharings validates that a share is priceable with
SELECT 1 FROM models WHERE provider = ?1 AND model = ?2, so listing a share of the new model was
rejected - the name was in neither config/config.example.toml nor the seeded models table.

Rename only, deliberately no alias handling: the retired names are dead and upstream-routed, and
"a deleted model bills 0" is the documented behaviour (admin.models.sub), so dropping them adds no
new defect class.

Related Issue

No issue exists for this - it was found from a direct report and upstream docs. Left empty on
purpose rather than fabricating one.

Changes

• config/config.example.toml: the flash row becomes deepseek-flash with the official prices
  (idle cache-hit 0.02 / uncached 1.0 / output 4.0 CNY per 1M; peak 0.04 / 2.0 / 8.0),
  vision = true (V4.1-Flash is natively multimodal), context 1M / max output 384K. The separate
  deepseek-v4-flash-vision-exp entry is folded into it, so the catalogue is now 13 models.

• ui/js/data.js: the MODELS / MARKET mirrors follow (13 models, 7 on sale).

• src/catalog_gate.rs: MODEL_COUNT 14 -> 13, KNOWN_MODEL / KNOWN_INPUT / KNOWN_OUTPUT
  updated to the new name and prices.

• src/config.rs, src/db.rs, src/routes/sharing.rs: fixtures and catalogue assertions updated.
  config.rs additionally asserts that the retired names are gone from the catalogue and that
  deepseek-flash is a vision model.

• docs/plan-api-matrix.md: stop hardcoding the catalogue size (it points at the single source of
  truth instead, so it cannot rot on the next change).

• ui/index.html: data.js cache-bust.

• Config/data-structure changes are mirrored into the example file

Tests

• cargo test all green - 239 passed / 0 failed (the count is unchanged: no test was added
  or removed, the catalogue assertions were updated in place)
• cargo fmt --check exit 0
• cargo clippy --all-targets -- -D warnings clean on CI's stable toolchain
  (main's latest run: step Run clippy = success). Disclosure: the only complete toolchain
  installable in the sandbox is rustc/clippy 1.95.0, whose clippy additionally reports one
  collapsible_match at src/protocol.rs:662 - pre-existing, out of this diff (landed in fix(protocol): give every announced responses item a unique output_index and its own order #207,
  green CI ever since) and therefore deliberately not touched here.
• Unit tests updated (catalogue assertions) - no new test was needed for a rename

A/B evidence

Two instruments. probe = the catalogue facts, read from the carriers and compared against the
official page (config [[models]], ui/js/data.js MODELS/MARKET, the doc); rust = the committed
cargo test suite, re-run against four trees.

leg	content	red set
v0_orig	pre-change catalog	{A1 A2 A3 A4 A5 A7 A8 A9} (probe)
m_add_only	the new name added, the old rows kept	{A4 A5 A7}
m_oldprice	the new name with the old price	{A2 A5}
m_novision	deepseek-flash without vision	{A3 A4 A7}
m_nobust	the catalogue edited but not the guest mirror	{A8}
R1_count	MODEL_COUNT left at 14	catalog_gate::tests::extractors_are_alive
R2_price	the flash row keeps the old price	5 tests: catalog_gate ×3, config::tests::parse_config_example_ok, db::tests::seed_models_upserts_from_config_models
R3_name	the flash row keeps the old name	11 tests: the 5 above + routes::sharing::tests ×6
live	the working tree	{} (239 passed)

The three Rust legs red pairwise-distinct sets and the mutated files were restored
byte-identically (md5 asserted before/after on both carriers). Note: the Rust legs were re-run with
the --quiet flag removed from the harness - libtest's --quiet prints one character per test,
which made every mutation leg read green (an A/B with no discriminating power). The corrected
harness also asserts that the parser actually saw per-test lines (239 in every leg), so a silent
parser can never report a green matrix again.

Checklist

• Branch naming follows the convention: fix/deepseek-flash-canonical-model
• Commit message uses Conventional Commits
• Single responsibility, minimal change

Deployment note

src/db.rs::seed_models is a full sync: [[models]] is authoritative and rows absent from it
are deleted at startup. Only the in-repo config.example.toml is edited here, so a running
deployment must apply the same rename to its own (gitignored) config.toml and restart so the
catalogue re-seeds. The retired names keep working upstream but are routed to V4.1-Flash and billed
at Flash prices, so keeping them listed would advertise a model that no longer exists.