feat(deploy): thread caller_path into deployers — bare-name deploy-time spawns still resolve against daemon PATH (follow-up to #1219)

[zackees]

Follow-up to #1219 / PR #1231, raised by CodeRabbit review there.

Problem

PR #1231 forwards the caller CLI's PATH per request and applies it to bare-name tool spawns on the build path (the five sites #1219 enumerated). The deploy path has the same class of exposure and was deliberately left out of that PR to keep it reviewable:

• BuildParams.caller_path is populated in the deploy handler, but only for the pre-deploy build. The Deployer trait API, deployer construction, and Deployer::deploy do not receive caller_path.
• Deploy-time helper spawns in fbuild-deploy pass env: None to the subprocess runners, so any bare-name fallback (e.g. the documented "falling back to esptool on PATH" path in esp32 deploy, see Orphaned mkdir install-locks deadlock after daemon crash; stale daemon endpoint survives 'daemon stop'; esptool provisioning failure kills daemon #1213 part 3) resolves against the daemon's spawn-time PATH — the exact staleness daemon binds tool resolution to spawn-time PATH for up to 12h — bare-name esptool/python/objcopy spawns resolve nondeterministically #1219 fixed for builds.
• The skip_build deploy path never constructs BuildParams at all, so caller_path currently has no carrier there.

Scope

1. Thread caller_path from the daemon DeployRequest (field already exists after fix(daemon): forward the caller CLI's PATH per request for bare-name tool spawns #1231) into deployer construction — likely a field on the deploy context/config struct rather than a Deployer::deploy signature change, whichever is less invasive given the trait's implementors.
2. Apply fbuild_core::subprocess::bare_name_path_overlay (added in fix(daemon): forward the caller CLI's PATH per request for bare-name tool spawns #1231) at deploy-time spawns that can run a bare name — audit fbuild-deploy for run_command/run_command_no_timeout calls with env: None where the program can be a bare fallback name. Provisioned absolute-path tools stay untouched (the helper no-ops for them).
3. Cover both the normal deploy path and skip_build.

Acceptance

• A deploy whose esptool provisioning fails resolves the bare-name fallback against the requesting CLI's PATH, not the daemon's.
• skip_build deploys carry caller_path the same way.
• Regression tests at the deployer-construction level for both paths.

Defaults chosen by the drafting agent are listed inline — edit as needed.

[zackees]

Claiming this — implementation starting now (session A, the one that authored #1240). If another session is already on it, comment here before opening a PR so we don't repeat the #1231/#1236 and #1240/#1242 duplicate-implementation collisions.

[zackees]

Retracting the claim above — this was already resolved by #1241 (merged 03:24Z, minutes before my survey); the closure hadn't propagated when I read the open-issues list. Validation of the merged implementation on current main is running (deployer builder tests + skip_build parity test); will follow up only if anything fails.