symposium-v0.4.0

Added

• inject update nudge into session-start hook additionalContext
• add self-update command and auto-update infrastructure

Fixed

• normalize CURRENT_VERSION in test snapshots for release compatibility
• use atomic rename in mock cargo install to avoid "Text file busy"
• rustfmt formatting and switch version check to cargo search

Other

• remove binary download, default auto-update to on, add init prompt
• auto-update re-exec for both sync and hook invocations
• end-to-end auto-update re-exec with mock cargo install
• snapshot output for update check tests with expect_test
• capture Output messages, assert update warning text
• move auto-update check into cli::run, add integration tests
• move cargo override from env var to Symposium field
• cargo search, cargo_command() helper, tests, hook update behavior
• SkillOrigin keyed on source location, readable Crate dirs
• demotion to suffixed names when a new origin introduces a conflict
• promotion to unsuffixed slot when origin conflict disappears
• only suffix skill dirs with origin hash on conflict
• dispatch on group source via single match in load_skills_for_group
• SkillOrigin::Git keys on (repo, commit_sha, skill_path)
• per-group disambiguator on SkillOrigin::Plugin; sha2 hash
• introduce SkillOrigin and dedup skill installs by origin
• add has_symposium_marker helper
• address review comments
• drop unimplemented 'distribution: workspace' section
• rewrite workspace-skills page
• Document workspace skills in user guide
• Add agents-syncing: mirror user-authored skills across agent dirs