docs: add 4.x feature roadmap

[DefinetlyNotAI]

Summary

Adds PLAN.md to document the planned Logicytics 4.x feature roadmap.

This change provides a single repository-level reference for upcoming 4.x work, intended feature direction, and planned development areas without changing runtime behavior.

User-visible result: contributors and maintainers can review the planned 4.x direction directly from the repository.

Contract impact

No runtime contract impact.

Verification

Documentation-only change. No live Windows probe is required because host behavior is unaffected.

• Relevant focused tests pass.
• python -m unittest discover -v passes.
• python -m compileall -q logicytics core tests passes.
• python -m logicytics preflight reports no invalid core collector.
• git diff --check passes.
• Live Windows integration tests pass when the change touches host behavior.

Review checklist

• I read CONTRIBUTING.md and searched for duplicate work.
• This pull request contains one coherent theme and conventional commits.
• Collector metadata, cancellation, isolation, and artifact registration remain valid.
• Configuration, output, migration, release, and feature-status docs are updated when affected.
• No generated evidence, credentials, private data, caches, or unrelated changes are included.
• I agree to the Developer Certificate of Origin and repository license.

Related issues

N/A

Summary by CodeRabbit

• Documentation
  • Added a roadmap outlining candidate features for Logicytics 4.x releases, including reporting, recovery, verification, and compatibility.
  • Linked the roadmap from the README.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Advanced

Run ID: 38f6bb19-4c43-4c13-83e4-496242654eab

📥 Commits

Reviewing files that changed from the base of the PR and between 8794250 and 7f0d733.

📒 Files selected for processing (2)

• PLAN.md
• README.md

Included review availability: This review used your included allowance. Your plan provides up to 1 included review per hour; 0 remain after this review.

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Walkthrough

The README links to a new roadmap for candidate features across versions 4.1.0 through 4.9.0. The roadmap lists planned features for those releases.

Changes

4.x Roadmap Documentation

Layer / File(s)	Summary
Roadmap and README link PLAN.md, README.md	PLAN.md lists candidate features for versions 4.1.0 through 4.9.0. The README links to the roadmap.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~3 minutes

Change: Other

Merge Risk: ⚪ Minimal · up to 7f0d7

The roadmap is discoverable from the README and clearly describes candidate plans; no concrete merge risk was identified.

Architecture Summary

Architecture risk: 🔵 Low · up to 7f0d7

The change affects 2 systems.

Changed systems: PLAN.md, README.md

Architecture concerns
No architecture-level concerns identified.

Review details

Systems and components

• observed — PLAN.md (service) was modified; 1 changed file maps to changed impact.
• observed — README.md (service) was modified; 1 changed file maps to changed impact.

Before / after behavior

• observed — Modified behavior in PLAN.md: Adds a roadmap table listing planned features for versions 4.1.0 through 4.9.0, including reports, metadata and audit trails, comparisons, plugin and offline-collection tooling, recovery, resource planning, integrity and export features, and contract and compatibility documentation.
• observed — Modified behavior in README.md: Adds a link to the 4.x roadmap for candidate features across the next nine 4.x releases.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the documentation change: adding a feature roadmap for the 4.x releases.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Commit to this branch
• Create a new PR

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_{Nine releases line up in a row
Reports and tools join the flow
Checkpoints, plans, and exports appear
Compatibility notes draw near
The README points the way
The roadmap maps what may come next day}

_{Comment @coderabbitai help to get the list of available commands.}