Argue from what survives, now that the official CLI is conversational

[ivanvyd]

Stacked on #36. Base is fix/complete-results-and-docs-contract; GitHub will retarget this to
main when #36 merges. Review #36 first.

The fact

Databricks CLI v1.10.0 — the version docs/compatibility.md already records as tested — ships:

databricks genie ask QUESTION [flags]
  -s, --session string    Session id (any string) to continue a conversation across calls
      --include-sql       Show SQL queries executed by the agent
  -o, --output type       text or json

Read from databricks genie ask --help on the installed binary, not from documentation.

ROADMAP.md named this event in advance: "The official CLI becoming conversational. The
differentiator would narrow to Question Packs and the .NET library, and the roadmap would follow."
It happened. This PR is the roadmap following.

What changes

README.md "Why this exists" is rewritten. It argued that this project exists because the
official CLI makes you manage six identifiers, a polling loop and a two-step download by hand. That
argument is now losable, so it is gone. What replaces it is the two claims that survive scrutiny:
Databricks publishes SDKs for Python, Java, Go and R but not .NET, and Question Packs have no
equivalent. The section now opens by pointing readers at databricks genie ask if a terminal
answer is all they want.

docs/decisions/0001 gains a dated correction, not a rewrite. The decision stands — still no
MCP server — but two premises do not:

• It claimed an MCP server would duplicate Databricks' managed endpoints. Those endpoints are
  stateless, so a stateful one would do the thing theirs cannot.
• It used that same statelessness as an argument against MCP, which confuses Databricks'
  implementation with the protocol.

The honest reason was always scope, and that is what the decision now rests on. GOVERNANCE.md and
ROADMAP.md are updated to say the same thing as the ADR rather than the superseded version.

ROADMAP.md moves the prediction into a dated statement that it occurred, rather than deleting
it. A project that predicts something, is right, and then says nothing has stopped paying attention.

NuGet version badges for both packages. Version only — a downloads badge on a package published
four days ago advertises a small number.

One claim I deliberately hedged

The official ask exposes no flag naming which Genie Agent answers — no space id argument, no
--space or --agent. The README says it "exposes no flag for" targeting a named Agent rather
than "you cannot choose the Agent", because its help text does not say how it resolves one and I
have not verified that behaviour.

Verification

223 tests pass. The docs-contract test added in #36 parses every lakespeak … example in the
rewritten README against the real command tree. All 40+ relative markdown links across the
repository resolve. Documentation-only otherwise — no source changes.