rpcperms+lncli: return gRPC status codes from RPC state interceptor

[kpshukla]

Summary

Fixes #5586

The checkRPCState interceptor previously returned plain Go errors, which gRPC forwarded to clients as codes.Unknown. Callers (including lncli) were forced to do brittle string matching against the error message to determine the cause.

This PR replaces each plain error return with a status.Error carrying a semantically correct gRPC code, while keeping the error message text identical to preserve any existing string-match code:

Condition	Before	After
LND still starting	codes.Unknown	codes.Unavailable
RPC server starting	codes.Unknown	codes.Unavailable
No wallet created	codes.Unknown	codes.FailedPrecondition
Wallet locked	codes.Unknown	codes.FailedPrecondition
Wallet already unlocked	codes.Unknown	codes.FailedPrecondition
Unknown state	codes.Unknown	codes.Unknown (unchanged)

The two lncli call-sites in cmd/commands/commands.go that checked codes.Unknown are updated to use codes.FailedPrecondition.

Test plan

• New table-driven test TestCheckRPCStateGRPCCodes covers all RPC states and server types (10 subtests, all pass)
• Existing rpcperms tests still pass
• make install compiles cleanly

🤖 Generated with Claude Code

[github-actions]

🟡 PR Severity: MEDIUM

gh pr view | 4 files | 146 lines changed (29 additions / 9 deletions excluding tests)

🟡 Medium (2 files)

• cmd/commands/commands.go - CLI client code (cmd/*); updates two call-sites to check codes.FailedPrecondition instead of codes.Unknown
• rpcperms/interceptor.go - not in a specially-categorized package; classified as "other Go file"

🟢 Low (2 files)

• rpcperms/interceptor_test.go - test-only change (new table-driven test, excluded from bump counting)
• docs/release-notes/release-notes-0.22.0.md - release notes entry

Analysis

The highest-severity files touched are cmd/commands/commands.go (CLI, explicitly MEDIUM per the classification rules for cmd/*) and rpcperms/interceptor.go, which doesn't fall under any of the CRITICAL/HIGH package prefixes (it's not lnwallet, htlcswitch, contractcourt, sweep, peer, keychain, input, channeldb, funding, lnwire, nor server.go/rpcserver.go), so it defaults to MEDIUM ("other Go files not categorized above").

The change itself is narrowly scoped: it maps existing plain errors in the checkRPCState interceptor to semantically correct gRPC status codes while preserving the original error message text, and updates two lncli call-sites to match. No bump conditions apply — only 3 non-test/non-doc files changed, and non-test lines changed (~38) are far below the 500-line bump threshold. No critical packages are touched at all.

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