feat(dnf): add read-only dnf tools and list output limits

[Albe83]

Summary

Adds read-only DNF tooling to the Linux MCP Server, enabling system diagnostics for RPM-based (RH-like) systems with DNF v4+. Includes list/detail workflows, repositories, groups and modules, plus safe output limiting for large datasets.

Changes

• Add DNF tools: list installed/available packages, package info, repo list/info, provides, groups, modules
• Enforce read-only execution and input validation
• Add list output controls (limit, offset, no_limit) with safe defaults and truncation note
• Update usage documentation
• Add comprehensive tests for all new tool paths and limits

Tests

• make verify

Notes

• Read-only by design (readOnlyHint=True)
• Output is kept raw to avoid early normalization
• Works on RH-like systems with DNF >= 4

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Flag	Coverage Δ
unittests	97.71% <100.00%> (+0.34%)	⬆️

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Files with missing lines	Coverage Δ
src/linux_mcp_server/commands.py	89.09% <ø> (ø)
src/linux_mcp_server/tools/__init__.py	100.00% <100.00%> (ø)
src/linux_mcp_server/tools/dnf.py	100.00% <100.00%> (ø)
src/linux_mcp_server/utils/validation.py	100.00% <100.00%> (ø)
tests/tools/test_dnf.py	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

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