docs: clarify customer guidance with public Entra ID terminology

[Hou (SciencePotato)]

What changed

Use public Microsoft Entra ID terminology consistently throughout the customer guides, including BYOT headings, caller authentication, payloads, responses, runtime READMEs, and optional multi-provider and Front Door guidance. Remove obsolete development-history anecdotes and references customers cannot use, while retaining practical provider requirements and the distinction between provider acceptance and recipient delivery.

The earlier customer-documentation improvements remain:

• Shorten the main setup walkthrough and stop embedding two obsolete terminal screenshots.
• Clarify recognized provider acceptance and the limits of verified Entra ID caller behavior.
• Use the saved certificate backing-secret identifier for reuse and replacement.
• Correct C# transport/extension locations, missing-provider response guidance, and an SMS wire example.
• Repair the monitoring table and explain the datetime-output requirement for repeated-violation alerts.
• Clarify unsupported setup overrides and the cost report's directory-role and masked-phone requirements.

Documentation only: scripts, runtime code, tests, dependency manifests, infrastructure, workflows, protocol fields, environment-setting names, and caller configuration are unchanged from main. The earlier launcher-help edit has been removed. The cost-guide change is a prerequisite clarification, not the separate hosting-price work in #50.

Review and verification

Completed sequential passes for terminology cleanup, accuracy/link/image consistency, and final public-language/rendering checks. Audited all 16 tracked Markdown guides plus help, comments, examples, release-template prose, and all 16 image assets.

• Rendered all guides and checked 433 local references, 14 image embeds, tables, and code fences.
• Checked six JSON, 18 PowerShell, and four JavaScript examples. This terminology update leaves fenced examples unchanged.
• Confirmed the BYOT guide remains provider-neutral and keeps the customer-owned integration steps. The simplified BYOT and sign-in guides contain no fenced code/configuration samples.
• Confirmed the final diff against main contains Markdown only. git diff --check passes.
• Ran 53 offline Python contract/handler checks successfully; no live identity or provider calls were made.

The BYOT title/response heading and evaluation heading now use public-facing wording; two obsolete BYOT aliases were removed. All current repository links resolve, but external deep links to the former headings or aliases need updating.

No image changes or new screenshots were needed: existing diagrams and portal examples already use public terminology. Existing source links and credits remain. No private exports or tenant data were accessed or published.

No Azure deployment, tenant changes, live Log Analytics queries, provider calls, or paid sends. This is static/offline review, not production certification or a guarantee of current Entra ID fallback behavior.

Ready for review; no merge requested.