feat(mdm): configurable install dir + persistent stderr logs

[shubham-stepsecurity]

What does this PR do?

Type of change

• Bug fix
• Enhancement
• Documentation

Testing

• Tested on macOS (version: ___)
• Binary runs without errors: ./stepsecurity-dev-machine-guard --verbose
• JSON output is valid: ./stepsecurity-dev-machine-guard --json | python3 -m json.tool
• No secrets or credentials included
• Lint passes: make lint
• Tests pass: make test

Related Issues

[Copilot]

Pull request overview

This PR centralizes “agent install directory” resolution and adds persistent on-disk stderr logging (with rotation) so diagnostic logs survive runs where telemetry can’t be sent.

Changes:

• Introduces internal/paths to resolve the base install directory from CLI/env/config with a legacy fallback.
• Adds internal/progress/filelog to tee stderr to agent.error.log (and rotates agent.log / agent.error.log at startup).
• Updates launchd/systemd/schtasks installers to bake STEPSECURITY_HOME so scheduled invocations use the same install directory.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
internal/telemetry/logcapture.go	Documents stderr-capture nesting behavior with the new file tee.
internal/systemd/systemd.go	Uses paths.Home() for log dir and injects STEPSECURITY_HOME into the unit.
internal/schtasks/schtasks.go	Uses paths.Home() and injects STEPSECURITY_HOME into the scheduled task command.
internal/schtasks/schtasks_test.go	Updates tests for new schtasks argument shape and log dir resolution path.
internal/progress/filelog/filelog.go	Implements stderr tee-to-file + best-effort rotation + eligibility checks.
internal/progress/filelog/filelog_test.go	Adds unit tests for teeing, rotation, skip behavior, and idempotent Stop.
internal/paths/paths.go	Adds install-dir resolution (CLI override/env/config/legacy).
internal/paths/paths_test.go	Adds tests for precedence and override behavior.
internal/launchd/launchd.go	Uses paths.Home() for LaunchAgent logs and injects STEPSECURITY_HOME into plist.
internal/config/config.go	Adds install_dir persistence and legacy-dir helpers.
internal/config/config_test.go	Adds JSON round-trip test for install_dir.
internal/cli/cli.go	Adds --install-dir parsing (including explicit empty to disable file logging).
internal/cli/cli_test.go	Adds coverage for --install-dir parsing and hooks acceptance.
internal/aiagents/cli/errlog.go	Routes hook error log location through paths.Home().
cmd/stepsecurity-dev-machine-guard/main.go	Installs filelog capture early, rotates logs, and warns about legacy leftovers.

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