refactor(orpc): standardize the single-record GET path (/show/{id} vs /{id})

[ciokan]

Moved out of studio/TODO.md (see #6).

some contracts have show while others have get: one or the other

Problem

The single-record GET route path is inconsistent across contracts:

Contract	Path
campaigns.ts:44	/show/{id}
leads_labels.ts:14	/show/{id}
projects.ts:11	/{id}
leads_lists.ts:12	/{id}
campaigns_sequences_versions.ts:47	/{id}

The procedure is named get in all of them; only the URL differs.

The /show/ segment is not arbitrary — contract/campaigns.ts:42 documents why:

// the /show/ segment is required, otherwise {id} would overwrite all other

A bare /{id} under a prefix that also has sibling static segments (e.g. /campaigns/sequences, /campaigns/counters, /leads/lists, /leads/labels) swallows those siblings. So /show/{id} is needed exactly where a router shares its prefix with sub-routers, and unnecessary where it doesn't.

Decision needed

Pick one and apply it everywhere:

1. /show/{id} everywhere — uniform and immune to future sub-routers being added under any prefix, at the cost of a slightly unusual REST shape.
2. /{id} where it is safe, /show/{id} only where a prefix collision exists — more conventional REST, but the rule is subtle and easy to break later (adding /projects/templates would silently break /projects/{id}).

Recommendation: option 1, for predictability — but that is the call to make here.

Scope

All of packages/orpc/src/contract/*.ts single-record GET routes, the matching apps/api/src/modules/** controllers, and any dashboard query files under apps/dashboard/src/tanstack/query/** that hit them. Rebuild packages/orpc afterwards. Also worth documenting the final rule in CONTRIBUTING.md / CLAUDE.md so it stops drifting.