docs: close UX gaps found reading every doc as a first-time user

[onelrian]

Overview

A full review of the released docs found real usability gaps: several places tell a reader what to do without saying how, exactly where precision matters most, and the troubleshooting table is too generic to act on.

Intent

The real intent of this issue is:

Docs that are accurate but too vague at the exact steps a reader needs (getting a NetBird token, creating the Kubernetes Secret every install example assumes exists) are functionally as unhelpful as wrong docs, since a real user gets stuck at the same place either way.

Source of Truth

• README.md and docs/INSTALLATION.md say "Create a NetBird personal access token" with no dashboard navigation steps.
• README.md, docs/INSTALLATION.md, and charts/auditbridge/README.md all reference envFromSecret.NETBIRD_API_TOKEN=netbird-audit/audit-token and -e NETBIRD_API_TOKEN_FILE=/run/secrets/netbird-token as if the underlying Secret/file already exists, with no kubectl create secret command anywhere.
• docs/SINKS.md documents generic sink variables as an abstract table with no worked example.
• docs/OPERATIONS.md's troubleshooting table says things like "Correct credentials or connectivity" without naming what to actually check.

Tasks

• Add exact NetBird access-token creation steps, sourced from NetBird's own docs
• Add the missing kubectl create secret commands everywhere a Secret is referenced
• Add a full worked example for a generic sink
• Rewrite the troubleshooting table with real log lines and metric names to check

Acceptance Criteria

• A first-time reader following any installation path (Docker, Compose, Kubernetes/Helm) has every command they need, nothing assumed to already exist
• Every claim in the troubleshooting table is checked against the real log/metric strings in the code, not written from memory

Definition of Done

• Acceptance criteria satisfied
• cargo test/clippy/fmt and helm lint all still pass
• No unresolved blocker remains