refactor(web): remove bootstrap project configuration

[Re1lya]

Summary

• remove the required ORA_PROJECT_NAME / ORA_PROJECT_PATH startup configuration and bootstrap project reconciliation
• stop creating a synthetic web/main project work context during server startup
• introduce WorktreeConfig for the useful worktree root and keep the existing project-work-context subsystem intact
• allow the web backend to become ready with an empty project catalog
• remove the obsolete project-name repository lookup and update tests, runtime documentation, and OpenSpec requirements

Why

The web runtime now supports multiple projects, so forcing one project into the database and into a fixed startup work context is no longer a valid ownership model. Projects should instead be created or added through the normal project APIs, while task operations continue to select their project and context explicitly.

Existing database projects are retained. This change only removes the fixed bootstrap chain and does not remove the project-work-context subsystem.

Configuration note

WorktreeConfig::from_database() currently derives the data directory from the parent of the SQLite database path. This is correct while both paths are governed by ORA_DATA_DIR, but it creates a small configuration coupling. If the database path becomes independently configurable, introduce an explicit DataDirectoryConfig and derive both DatabaseConfig and WorktreeConfig from it.

Checks

• cargo fmt --all
• task test
• cargo clippy -p ora-web-server --all-targets -- -D warnings
• cargo clippy --workspace --lib --bins -- -D warnings
• RUSTDOCFLAGS='-D warnings' cargo doc -p ora-web-server --no-deps

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