feat(sequence-numbering): Implement sequence numbering command with comprehensive specifications

- Removed obsolete tasks.md from 001-sequence-numbering.
- Added detailed requirements checklist for sequence numbering command.
- Created OpenAPI contract for sequence command, defining preview and apply endpoints.
- Developed data model for sequence numbering, outlining key entities and their relationships.
- Drafted implementation plan for sequence numbering command, including project structure and complexity tracking.
- Compiled quickstart guide for sequence numbering command, detailing prerequisites and usage examples.
- Documented research findings related to command validation, ordering, and conflict handling.
- Established feature specification for sequence numbering command, including user scenarios and acceptance criteria.
- Created tasks.md for 007-sequence-numbering, outlining phases and implementation strategy.

specs/007-sequence-numbering/quickstart.md

@@ -0,0 +1,55 @@
+# Quickstart: Sequence Numbering Command
+
+## Prerequisites
+- Go 1.24 toolchain installed.
+- `renamer` repository cloned and bootstrapped (`go mod tidy` already satisfied in repo).
+- Test fixtures available under `tests/` for validation runs.
+
+## Build & Install
+```bash
+go build -o bin/renamer ./cmd/renamer
+```
+
+## Preview Sequence Numbering
+```bash
+bin/renamer sequence \
+  --path ./fixtures/sample-batch \
+  --dry-run
+```
+Outputs a preview table showing `001_`, `002_`, … prefixes based on alphabetical order.
+
+## Customize Formatting
+```bash
+bin/renamer sequence \
+  --path ./fixtures/sample-batch \
+  --start 10 \
+  --width 4 \
+  --number-prefix seq \
+  --separator "" \
+  --dry-run
+```
+Produces names such as `seq0010file.ext`. Errors if width/start are invalid.
+
+## Apply Changes
+```bash
+bin/renamer sequence \
+  --path ./fixtures/sample-batch \
+  --yes
+```
+Writes rename results to the `.renamer` ledger while skipping conflicting targets and warning the user.
+
+## Undo Sequence Batch
+```bash
+bin/renamer undo --path ./fixtures/sample-batch
+```
+Restores filenames using the most recent ledger entry.
+
+## Run Automated Tests
+```bash
+go test ./...
+tests/integration/remove_flow_test.go    # existing suites ensure regressions are caught
+```
+
+## Troubleshooting
+- Conflict warnings indicate existing files with the same numbered name; resolve manually or adjust flags.
+- Zero candidates cause a 409-style error; adjust scope flags to include desired files.