Modernization Phase 1.5: lint remainder — clangd-tidy from PyPI, suppressions triaged to zero

[ptesavol]

Phase 1.5 closes the lint workstream. Two deliverables:

1. clangd-tidy: git submodule → pinned PyPI install

The submodule pinned tag 0.2.1 (the single-script era). Upstream 1.x is a proper Python package with dependencies (attrs/cattrs/typing-extensions), so a bare checkout is no longer runnable at all — "bump the submodule" was not an option.

• Submodule deleted; install-prerequisities.sh now does pipx install --force clangd-tidy==1.1.1 on both platforms (pipx: preinstalled on GitHub runners, brew/apt otherwise; ~/.local/bin added to PATH).
• The 10 lint.sh call sites invoke clangd-tidy from PATH; the unused clang-tidy symlink alias is gone.
• Gained since 0.2.1: --line-filter clang-tidy parity, diagnostic-formatter fixes, clangd-tidy-diff.

2. .clang-tidy suppression triage: zero suppressions kept

All 11 post-18 check suppressions parked in Phase 1.2 are removed — every finding fixed in code rather than suppressed. 85 findings total (77 from the sweep, 7 more exposed by also dropping the nested test configs' copy, 1 introduced by the ranges conversion itself and fixed):

Check	n	Fix
readability-container-contains	28	find() != end() → contains(); two substring cases became C++23 std::string::contains
modernize-use-designated-initializers	29	aggregates name their fields
modernize-use-ranges	9	std::ranges:: algorithms (+1 explicit ptrdiff_t cast: ranges::sample takes a signed count)
readability-avoid-return-with-void-value	6	return voidFn(); in void lambdas → plain call
bugprone-suspicious-stringview-data-usage	4	env-var name constants were string_views passed to getenv(.data()) — now const char* (the honest type for a null-terminated-string API)
readability-redundant-casting	3	static_cast<const DhtCallContext&> of a const DhtCallContext& deleted
bugprone-unused-local-non-trivial-variable	3	dead debugString debug leftovers deleted
performance-enum-size	2	ConnectionManagerState, Offerer → : std::uint8_t
bugprone-optional-value-conversion	1	optional→value→optional round-trip → direct optional assignment
readability-use-std-min-max	1	clamp-if → std::min
modernize-use-starts-ends-with	1 (+1 in triage)	find() == 0 → starts_with

Several of these touch runtime code paths (ConnectionManager, WebsocketServer, logger internals), hence the full-suite gate below.

Verification

• Full rebuild + ./lint.sh green across all 8 packages — all checks enabled, clangd-tidy 1.1.1 from pipx
• 307/307 tests passed
• clang-format at fixed point; formatting included in the same commit since nearly every formatted hunk is a fixed finding

Remaining in Part 1

Only Phase 1.6 (CI/docs closeout — small). Then Part 2: the modules migration.

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