Retire stale ROADMAP.md and move durable architecture to scoped docs

## Problem

`ROADMAP.md` is no longer a reliable planning source for the .NET SDK:

- `v0.14.0-preview.1` ships 98 generated connector clients, while the roadmap still reports only two connectors with actions.
- It marks shipped clients such as Office 365 Users, Excel Online Business, Salesforce, DocuSign, and Event Hubs as not started or unevaluated.
- Its execution plan still includes completed work such as NuGet installation guidance and generated Microsoft connectors.
- It mixes .NET SDK work with Functions-extension, LSP UI, Python, Node.js, Java, connector-service, and conceptual-documentation ownership.
- The issue tracker and release changelog now provide more current, reviewable status.

Maintaining a second, manually synchronized status inventory is creating misleading guidance rather than planning value.

## Proposed change

Retire the root roadmap instead of attempting another full status rewrite:

1. Move any durable trigger architecture or settled design decisions that exist only in `ROADMAP.md` into `docs/triggers.md`.
2. Move durable connection-setup architecture, if any is unique, into `docs/connection-setup.md`.
3. Delete connector rollout tables, dated execution checklists, success metrics, and cross-repository plans that are represented by shipped code, README inventory, or GitHub issues.
4. Delete `ROADMAP.md` and remove repository links to it.
5. Use GitHub issues, labels, and focused design documents as the planning source of truth.

## Acceptance criteria

- No unique, still-valid architectural decision is lost.
- `ROADMAP.md` and all links to it are removed.
- `README.md` remains the shipped connector inventory.
- `docs/triggers.md` contains the current trigger status and architecture without dated implementation checklists.
- Open work is represented by scoped GitHub issues with owners or dependency labels.

Start by reviewing ROADMAP.md alongside README.md, docs/triggers.md, and docs/connection-setup.md, then search the repository for links to ROADMAP.md. Preserve only durable architecture and current trigger status, remove outdated planning material, and verify the acceptance criteria: no valid decisions are lost, README.md remains the connector inventory, and open work is represented by scoped issues.

Written by the indexing model from the issue text.