Rewrite roadmap into realistic MVP-ready issue backlog

[TheZupZup]

Motivation

• Make planning honest and actionable by aligning the roadmap with the repository's current, working surfaces.
• Lower contributor friction by turning aspirational items and placeholders into immediate, startable issues.

Description

• Replace the previous high-level ROADMAP.md with a reality-based backlog that lists 5 concrete, MVP-style issues (dev/test workflow, GTK entrypoint cleanup, blocklist wording, memory stabilization, and placeholder module decisions).
• Each issue includes Overview, What needs to be done, Goal, and Notes, and small tasks are labeled good first issue while broader stabilization items are help wanted.
• This is a documentation-only change to ROADMAP.md and does not modify runtime behavior or application code.
• Large or risky features (firewall backends, automated kills, service-level rule engines) are explicitly deferred in the new document.

Testing

• Ran pytest -q in the repo root, which failed during collection with ModuleNotFoundError: No module named 'silentguard'.
• Ran PYTHONPATH=src pytest -q, which failed due to a missing runtime dependency (ModuleNotFoundError: No module named 'psutil').

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Codex Task