docs: add project documentation

TASKLIST.md

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+# Task List
+
+Active, prioritized work items.
+
+## In Progress
+
+(none)
+
+## Next Up
+
+| # | Task | Notes |
+|---|------|-------|
+| 1 | Unit tests for `client.resolve_digest()` | Core function, good test candidate |
+| 2 | Unit tests for `client.build_url()` | Simple, deterministic |
+| 3 | Mock API tests for `commands.cmd_projects()` | Start with simplest command |
+| 4 | Unicode status symbols in output | Replace dashes with box-drawing |
+| 5 | Add `--quiet` mode for scripting | Suppress headers, minimal output |
+
+## Backlog
+
+| Task | Phase |
+|------|-------|
+| ANSI color support (with NO_COLOR) | 3 |
+| JSON output mode for all commands | 3 |
+| `labels` command | 4 |
+| `copy` command | 4 |
+| `quota` command | 4 |
+| pyproject.toml with entry points | 5 |
+| Shell completions | 5 |
+
+## Completed
+
+- [x] Initial implementation
+- [x] CI pipeline setup
+- [x] Empty response body handling fix
+- [x] README documentation
+- [x] PROJECT.md, ROADMAP.md, TODO.md created
+- [x] Type hints for `api_request()` and `load_credentials()`
+- [x] `--version` flag (`-V`)
+- [x] `build_url()` helper function
+- [x] `--verify-ssl` flag for SSL certificate verification
+- [x] Modular package structure (`src/harbor/`)
+- [x] Documentation updated for new structure