feat(landing): count registered maintainers' merged PRs in repo activity

[e35ventura]

Problem

Several repos on the landing grid showed "0 prs merged this week" despite real, ongoing work — mini-router/minirouter had 8 PRs merged in the last 7 days on GitHub but read as dead.

The cause: the activity digest is built from /prs, and the scoring pipeline deliberately excludes maintainer-authored PRs from that feed (maintainers are paid through the repo's maintainer_cut carve-out, not per-PR scores). Any repo where the maintainer ships their own work undercounts, all the way down to zero.

Fix

New useMaintainerMergedPrs hook recovers those PRs from the mirror and folds them into the landing-page digest (weekly count, sparkline, active miners). A maintainer's merges count only when the account is both:

• listed by the mirror as a maintainer of a repo with maintainerCut > 0, and
• registered as a miner UID

— the same conditions under which the carve-out actually pays them. Merges only count toward repos the account maintains (their contributions elsewhere already flow through /prs), and are deduped by PR number against the feed.

Cost: ~26 extra mirror requests on landing load (15 maintainer lookups + 11 pull feeds), cached 5 minutes via react-query. Mirror failures degrade to feed-only counts rather than blocking the digest.

Before / after

	Before	After
minirouter (maintainer tmimmanuel, UID 244, 30% cut)
vouch

Verified against live data (2026-07-20)

Weekly counts that change, simulated with the exact fold logic against prod APIs:

repo	feed only	with maintainers
mini-router/minirouter	0	8
vouchdev/vouch	1	30
phase-rs/phase	88	207
gittensor-model-hub/sparkdistill	20	61
gittensor-ai-lab/sparkinfer	18	25
gittensor-vanguard/vanguarstew	71	81
jsonbored/loopover	517	851
jsonbored/metagraphed	443	800
jsonbored/awesome-claude	307	314
we-promise/sure	3	6

touchpilot and das-github-mirror still show 0 — correct: GitHub confirms neither merged a PR in the last 7 days.

Note for local dev: VITE_REACT_APP_MIRROR_BASE_URL must be set (it's in .env.example but not .env), otherwise all mirror-backed features — including this one — silently no-op.