feat(logs): daily rotation + timestamps for raw stream log

[janstol]

Summary

The LaunchAgent launcher previously redirected all stdout/stderr into a single, ever-growing ~/logs/mcptask_runner/<slug>.log with no timestamps.

• Adds lib/mcptask_runner/log_filter.rb, a stdlib-only stdin→file filter piped from the generated launcher script.
• Timestamps only entry-start lines (e.g. [Claude], [EventStream]) so multi-line pretty-printed JSON bodies stay readable — indented lines (including nested JSON arrays like [) are left untouched.
• Rotates into a daily file per project: ~/logs/mcptask_runner/<slug>/YYYY-MM-DD.log.
• Filter is invoked with plain ruby (not bundle exec) from a stable helper-bin path copied in by the installer, so logging survives even while the launcher is healing a broken/stale bundle.
• set -o pipefail keeps the launcher's exit status reflecting the rake task rather than the filter.

Migration

Existing installs need bundle exec rake mcptask_runner:install FORCE=1 to pick this up. Old flat <slug>.log files are left in place, harmless.

Test plan

• ruby bin/ci — all green (tests, RuboCop, Reek, Flay)
• New test/services/log_filter_test.rb covers decorate (entry lines, JSON bodies, blank lines, indented nested arrays), dated_path, and end-to-end rotation across a day boundary
• Updated test/services/installer_test.rb for the new launcher script shape (pipe instead of exec >>) and log filter installation
• Manual: piped sample [Claude]/[EventStream] lines through the filter and confirmed correct timestamping + file placement