* Wire disk-pressure self-heal into the Tentacle host lifecycle

The self-heal scaffolding (SelfHealController, DiskPressureHealAction,
DefaultWorkspaceCleanupPolicy, and their tests) was built but never
scheduled — TentacleFlavor returned BackgroundTasks = [], so a disk-full
agent failed every deployment via LocalScriptService's admission gate
with no auto-reclaim of completed-script workspaces.

Wire it:
- WorkspaceProbe enumerates {tempRoot}/squid-tentacle-{ticketId} dirs and
  classifies each from its persisted ScriptState — Complete+0 => Succeeded,
  Complete+nonzero => Failed, started-not-complete => Active, no state =>
  Unknown — plus recursive size + last-write, so the cleanup policy can pick
  oldest-evictable workspaces while protecting a retention window.
- SelfHealBackgroundTask adapts SelfHealController to the host's
  ITentacleBackgroundTask lifecycle (Start on launch, drain on shutdown);
  ForLocalWorkspaces builds the disk-pressure action over the temp root with
  the running script backend as the live-workspace veto.
- TentacleFlavor now schedules it (BackgroundTasks = [selfHeal]).

The running-script reporter veto means an in-flight deployment's workspace
is never swept; only completed/orphaned workspaces are reclaimed, and only
under disk pressure.

Tests:
- WorkspaceProbeTests: real temp dirs + real ScriptState files — status
  classification matrix, prefix filtering, size, missing-root
- SelfHealBackgroundTaskTests: RunAsync starts the heal loop + drains on cancel
- TentacleFlavorSelfHealWiringTests: the flavor schedules a SelfHeal task
  (the dead-code-is-now-live regression guard)

* Harden disk self-heal: retention TTL floor, symlink-safe sizing, corrupt-state reclaim, backoff

The wiring that takes the disk self-heal live (the 30s DiskPressureHealAction over
{tempRoot}/squid-tentacle-*) is a second sweeper over the same directories the
24h orphan sweep owns, and the probe/policy had several robustness gaps. Address
them before the sweep runs in production:

- Honour the operator's orphan-workspace TTL as a retention floor: under mild
  (non-critical) pressure the new sweep no longer evicts inside the post-mortem
  window the existing age-based orphan sweep promises; under critical pressure the
  floor is bypassed so reclaiming disk still wins.
- Protect a just-created workspace via a 60s fresh-grace floor (even under
  critical pressure), closing the StartScript TOCTOU gap between CreateDirectory
  and the first state Save / running-script registration.
- Classify a present-but-corrupt state file as Unknown instead of skipping the
  workspace forever — otherwise a dead-but-corrupt workspace is permanently
  un-reclaimable, exactly when disk pressure most needs the space.
- Skip reparse points in the recursive size walk so a directory symlink (extracted
  package or runtime ln -s) cannot loop the enumeration or mis-attribute a
  symlink target's size to the workspace.
- Warn once + back off exponentially when a sweep reclaims everything it is
  allowed to but the disk stays under pressure (non-workspace usage), instead of
  churning every 30s.
- Expose the retention counts + low-disk trigger behind env vars with pinned
  const names (SelfHealOptions), mirroring the orphan-TTL env-var pattern.

All floors default off in DefaultWorkspaceCleanupPolicy/DiskPressure so the
parameterless constructors behave exactly as before; only the live
ForLocalWorkspaces wiring injects them — non-breaking.

Tests: SelfHealOptions env-var/default pins; corrupt-state, recursive nested-size
and symlink-safety probe cases; non-critical-TTL + critical-bypass + fresh-grace
policy cases; backoff growth/cap/reset; and a high-fidelity wired-chain E2E
(real probe + policy + ScriptStateStore + Directory.Delete) proving real reclaim
while a Running workspace and the in-TTL window survive.

* Pin SelfHealOptions bounds + parse branches, invariant-culture percentage parse

Make MinKeepCount/MaxKeepCount public (mirroring LocalScriptService's orphan-TTL
bounds) and extract the env-value parsing into internal testable helpers so the
reject/fallback branches are directly pinned (Rule 9 branch coverage). Parse the
free-percentage with invariant culture so an operator's '0.20' reads the same on a
comma-decimal locale server.