Add Insta360 Link 2C detection and model support

[p0ns]

Summary

Recognize the Insta360 Link 2C (2e1a:4c03) and enable the existing shared controls without treating this fixed-lens model as a motorized Link 2.

• Add model identification/name and an optional udev rule.
• Allow the shared Link 2 tracking control path while retaining its extension-unit GUID check.
• Mark the 2C as having no gimbal: reject misleading pan/tilt controls and omit their ranges instead of accepting firmware's dummy controls.
• Keep the broad hardware-validation flag off; not every feature has been validated.
• Adapt opt-in hardware tests to account for non-motorized models.

This PR deliberately does not introduce digital framing commands. A dependent follow-up adds those separately.

Hardware evidence

A physical camera is detected as:

1  Insta360 Link 2C  /dev/video0  2e1a:4c03

The camera owner manually verified zoom, focus, white balance, and brightness. Read-only checks also pass for status, info, and tracking. Pan/tilt are intentionally unsupported because the Link 2C has no motorized gimbal; successful firmware reads were not evidence of movement support.

Validation

Tested the exact standalone contents of this first commit, separately from the digital-framing working tree:

• cargo fmt --check
• cargo test — 65 passed
• cargo test --features hardware-tests -- --ignored readonly — 4 passed on the connected Link 2C
• cargo clippy --all-targets --all-features -- -D warnings

[p0ns]

Stacked follow-up: #2 adds digital framing separately and is a draft until this foundational model-support PR is merged. Framing-only review: p0ns/linkctl@feat/link2c-support...feat/link2c-digital-framing