chore(lab): scope the bench to the repository and remove the campaign

[luuuc]

Nothing in the Sense binary changes. This is the bench instrument, and it gets
one idea smaller: a repository is the unit of work. Benching one now takes a
single command with no setup decision in front of it, and the spend ceiling
that was written down but never enforced now actually stops a paid run.

Problem

sense-lab carried a container above the repository called a campaign, and it
required one before anything could happen: sense-lab repo mastodon/mastodon
refused with -campaign names the run tree the index artifact belongs to. That
is a decision demanded before it can be informed, in the run path, on a crank
that is supposed to run unattended.

The container held no fact of its own. Its spend ceiling was never enforced
(budget.Ceiling had no caller outside its own test), its arm matrix drove
nothing (plan.Expand has one caller, which prints a table), and its judge pin
has no consumer. Everything it grouped was already per repository: the run
tree, the authoring cycles, the position, the verdicts, the attempts. What was
left was a directory name, and it made the instrument harder to explain than
the thing it measures.

Summary

Removes the campaign and scopes the bench to the repository: its own run tree,
its own arms, its own spend ceiling of 40 paid runs, which probe now refuses
to spend past.

Changes

Admission and position

• sense-lab repo drops -campaign. Run trees live under runs/repos/<id>,
  reached by -runs with a default nobody needs to type. The original
  invocation now works: sense-lab repo owner/name resolves, clones, pins,
  scans and records.
• sense-lab status drops -campaign for -runs and reports every repository
  under it, each with its own spend against its own ceiling.

The bench matrix

• plan.Campaign becomes plan.Bench, losing Key and Repos. One
  repository, its subjects, its arms, its pinned judge.
• sense-lab plan -campaign <key> becomes sense-lab plan -repo <id>, reading
  lab/benches/<id>.json instead of lab/campaigns/<key>/campaign.json.

The spend ceiling, wired

• 40 paid runs per repository over its lifetime, refused by probe before
  anything spawns. It is read off the tree on every call rather than counted in
  memory, so a loop resumed after a crash cannot spend the budget twice.
• budget.ErrCeiling is a sentinel, so a refusal is tellable from a tree that
  could not be read. probe answers with its refusal code rather than its
  error code.
• No flag raises it, and status lost its -ceiling flag: one constant feeds
  the page and the refusal, so the page cannot state a ceiling nothing holds.

Correctness found on the way

• The handoff phase declared reads: campaign.json, a file that has never
  existed in any run tree. It now declares attempts/, which is what the plan
  actually reads.

Architecture Highlights

• budget.Read is unchanged. It always walked whatever root it was handed, and
  only its argument moved from a campaign to a repository, which is the sign
  this was a naming convention rather than a mechanism.
• Records stay global at runs/records/ rather than moving under a repository.
  A finding is about a Sense surface, not about the repository it was seen in,
  and scattering findings per tree is the exact failure the record package was
  built to close.
• The bench matrix is its own file next to the repository file, not a block
  inside it. The two have different authors and lifetimes: what a repository is
  gets written by admission, how it is measured gets written by a person.

Breaking Changes

⚠️ Local only, and the lab ships no repositories or campaigns, so there is
nothing to migrate in this repo.

• sense-lab repo -campaign <dir> is gone. Drop the flag.
• sense-lab status -campaign <dir> becomes sense-lab status (or -runs).
• sense-lab status -ceiling <n> is gone.
• sense-lab plan -campaign <key> becomes sense-lab plan -repo <id>, and
  lab/campaigns/<key>/campaign.json becomes lab/benches/<id>.json with
  repo in place of key and no repos list.
• An existing run tree at runs/campaigns/<key>/<repo> moves to
  runs/repos/<repo>, and its records/ moves to runs/records/. No code
  migrates it, and nothing reads the old path.

Test Plan

• A probe past 40 paid runs is refused with the refusal code, before a cell
  directory is created
• A neighbouring repository's 40 paid runs do not stop a repository that
  has spent nothing
• Spend is reported per repository: two paid runs on one and one on
  another, with mini-bench runs excluded as unpaid
• A ceiling refusal is identifiable via errors.Is, so it cannot be
  confused with an unreadable tree
• status reports the default root without being told, and rejects
  -ceiling
• A bench file naming a different repository than the one it is filed under
  is refused, as is an unknown field in it
• sense-lab repo -show mastodon/mastodon resolves, prints the position
  and exits with the shown code, with no campaign anywhere
• go test ./... passes
• make ci green: per-file coverage gate passes, 96.1% total, 0 lint
  issues, complexity ledger at 0
• qlty check reports no issues, with no smells in any changed file
• sense and sense-lab binaries build cleanly

[codecov]

Codecov Report

❌ Patch coverage is 96.66667% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
lab/internal/cli/probecmd.go	81.81%	1 Missing and 1 partial ⚠️
lab/internal/status/status.go	89.47%	1 Missing and 1 partial ⚠️

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