fix: inherit environment in daemon subprocess calls (#876)

The daemon's exec.Command calls were not explicitly setting cmd.Env,
causing subprocesses to fail when the daemon process doesn't have
the expected PATH environment variable. This manifests as:

  Warning: failed to fetch deacon inbox: exec: "gt": executable file not found in $PATH

When the daemon is started by mechanisms with minimal environments
(launchd, systemd, or shells without full PATH), executables like
gt, bd, git, and sqlite3 couldn't be found.

The fix adds cmd.Env = os.Environ() to all 15 subprocess calls across
three files, ensuring they inherit the daemon's full environment.

Affected commands:
- gt mail inbox/delete/send (lifecycle requests, notifications)
- bd sync/show/list/activity (beads operations)
- git fetch/pull (workspace pre-sync)
- sqlite3 (convoy completion queries)

Fixes #875

Co-authored-by: Jackson Cantrell <cantrelljax@gmail.com>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

internal/daemon/daemon.go

@@ -1101,6 +1101,7 @@ Manual intervention may be required.`,
 
 	cmd := exec.Command("gt", "mail", "send", witnessAddr, "-s", subject, "-m", body) //nolint:gosec // G204: args are constructed internally
 	cmd.Dir = d.config.TownRoot
+	cmd.Env = os.Environ() // Inherit PATH to find gt executable
 	if err := cmd.Run(); err != nil {
 		d.logger.Printf("Warning: failed to notify witness of crashed polecat: %v", err)
 	}