feat(modules): add fingerprint module type

[TBX3D]

a fingerprint module identifies a technology by weighted body/header signatures scored into a confidence, with an optional version regex, rather than a boolean match. it fires one finding carrying the score once it reaches the threshold (default 0.5) - the framework detectors' scoring approach, in the module format, so a custom tech fingerprint can live alongside other modules. validated at load (signatures present, non-empty patterns, finite weights, confidence in [0,1], version regex compiles) and covered by yaml round-trip, validation, header, version and default-threshold tests. documented in docs/modules.md.

depends on #355: the first two commits here are that PR's shared sifpath/httpx helpers (fingerprint.go uses httpx.ReadCappedBody), included so this branch builds standalone. once #355 merges, rebasing this one should drop those two commits as already-applied and leave only the fingerprint commit.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 79.56989% with 19 lines in your changes missing coverage. Please review.
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Files with missing lines	Patch %	Lines
internal/modules/fingerprint.go	80.23%	9 Missing and 8 partials ⚠️
internal/modules/yaml.go	71.42%	1 Missing and 1 partial ⚠️
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Additional details and impacted files

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##             main     #356   +/-   ##
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  Coverage        ?   65.04%           
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  Files           ?       89           
  Lines           ?     7951           
  Branches        ?        0           
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  Hits            ?     5172           
  Misses          ?     2378           
  Partials        ?      401           

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[github-actions]

pr summary

6 files changed (+494 -15)

category	files
go source	5
tests	2

[vmfunc]

scoring lines up with the framework detector's MatchSignatures, and the boundary's right: score == threshold fires, 0.4 body-alone stays quiet. validation covers the nan/inf weight and regex-compile cases too, good.

two non-blocking notes:

• version + evidence are both body-only. scoreFingerprint runs the regex on body, and the finding's evidence is truncateEvidence(bodyStr). so a header-scoped fingerprint like your acme example can't pull a Server: nginx/1.2.3 version, and the evidence won't contain the thing that actually matched. worth a follow-up, a lot of real fingerprints are server-header versions.
• no user-agent on the probe, the http executor sets sif/1.0. some hosts vary or block on go's default UA, so this can move detection accuracy. cheap to add.

confidence: 0 quietly becomes 0.5 via the == 0 check so you can't express always-fire, minor corner. in.

[TBX3D]

rebased. #355 merged, so the two shared-helper commits this was stacked on dropped as already-upstream and the branch is just the fingerprint module type now. the only resolution was the docs type line, which lists http, tcp and fingerprint.