feat(quota): admin-granted paid plans via wallet PlanOverride (no Stripe)

[lukemarsden]

Admins could only Activate Trial (a Stripe trial sub), which is wrong for a customer who paid out-of-band (bank transfer, no card): it's time-limited, Stripe-managed (so a manual fix gets reverted by Stripe sync — exactly what happened when I bumped find-ai to active and a webhook put it back to trialing), and ties the account to a trial lifecycle. find-ai/Leah hit all of this.

Adds a Stripe-independent plan grant:

• Wallet.PlanOverride ("pro"|"free"|"") — quota honors it over the Stripe-derived tier in both the org and user paths. Stripe sync only ever writes subscription_*, never PlanOverride, so an admin grant can't be reverted by a webhook.
• POST /admin/orgs/{id}/plan — set an existing org's plan.
• Activate-with-plan — grant a paid Pro plan (override, no Stripe) as an alternative to the trial; if the user has no org yet it stashes PlanOnFirstOrg, consumed onto their first org's wallet (consumeUserPlanOnFirstOrg, next to the existing trial/credit consumers in org creation).
• Frontend: AdminOrgsTable gains a Plan column + set-plan menu (Pro / Free / clear); the Activate dialog gains a plan selector (Trial vs Paid Pro). Regenerated API client + swagger.

Testing

• Unit (quota_test.go): PlanOverride=pro → Pro with no subscription; =free forces Free even over an active sub. go test ./pkg/quota/ green.
• go build ./pkg/server/ clean; yarn build clean.
• Not yet live-exercised end-to-end (ships via release); meta E2E after merge: set a test org to Pro in the admin Orgs UI → GetQuotas returns Pro; confirm a Stripe sync does not change the override.

Once this ships, find-ai gets a proper paid plan (PlanOverride=pro) instead of the spurious trial, and the same admin control covers every out-of-band-paid customer.

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