docs: link the four remaining website guides from the README

[DennisAlund]

Completes the README side of the website guide programme. Four Meta links had no Flutter-specific answer beside them; now all six published guides are linked from the problem they solve.

What changed

Location	Meta link (kept)	Guide added
Documentation list	rhg	fbae-guide-app-events
Setup step 2, client token	jex	fbae-guide-client-token
Swift Package Manager	s73	fbae-guide-spm
Dependencies on Facebook SDK	ikt, un7	fbae-guide-sdk-versions

Six lines added, one line modified. No code, no version change.

Rules followed

• Both links, always. Meta's page stays visible next to every guide link.
• The README keeps the verdict. Each addition sits after the README's own answer, so a reader who never clicks is still unblocked.
• Link text says what is behind it, rather than "see the guide".
• No conversion links at the top. The tagline on line 9 also points at rhg and is deliberately untouched: positioning, not a documented problem.

Measurement integrity

The existing shortlinks ikt, un7, s73, jex and rhg are unchanged. Every slug carries its own click counter, so reusing a README slug on the website, or a guide slug in the README, would merge guide click-through into the README baselines for exactly the destinations these guides exist to displace. The four fbae-guide-* slugs were all at 0 clicks when this branch was cut, giving a clean before-number for the 30-day read.

Verification

• All six guide pages return 200 with bodies of 147 to 184 KB, so none is a soft 404.
• All four fbae-guide-* slugs exist as custom primary slugs pointing at the right guide URLs. Checked through the shortener API, not by fetching the slugs, so no counters were polluted.
• The three previously retracted claims stay absent: no suggestion that either codeless debug flag does anything, no claim that requests against a removed Graph API version fail, no claim that the plugin handles ATT, consent or privacy compliance. The "codeless events should still work" hedge is intact.
• No em dash in any added line.

Note for the maintainer

docs/WEBSITE-HANDOFF-2.md states "No Co-Authored-By trailer in commit messages, per this repo's CLAUDE.md". CLAUDE.md does not say that, and recent commits (995e069, 09902dc, 3ab9184) all carry the trailer. This commit follows the handoff and omits it, per maintainer decision. Worth either recording the rule in CLAUDE.md or correcting the handoff, so the next person does not hit the same ambiguity.

[Copilot]

Pull request overview

This PR updates the repository README to link four remaining Flutter-specific website guides next to the corresponding existing Meta documentation links, completing the README-side cross-linking for all published guides.

Changes:

• Adds a Flutter-specific guide link alongside the Meta “App Events overview” link in the Documentation section.
• Adds Flutter-specific guide links for: client token placement/diagnosis, Swift Package Manager setup, and resolved Facebook SDK version behavior.

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