fix(pr): cap the needs-repair reason on pr repair and pr dash

[cameronsjo]

Summary

RepairReason is built from subprocess error text, so it can be any length. pr repair and pr dash both printed it whole. That's one physical line, but it can wrap the terminal many times.

• New termsafe.SafeLineMax(s, maxRunes): this is SafeLine capped by rune count.
  • The cap counts escaped output, so a run of control characters can't grow past it.
  • It cuts only between whole escapes. A `` is kept or dropped entire, never split into misleading text.
  • A cut value ends in TruncatedMarker ( … [truncated]).
• One helper, repairReasonLine, feeds both sinks, so pr repair and pr dash show the same 200-rune text.
• pr repair --json still carries the full value.
• SafeLine now shares a per-rune safeRune helper with SafeLineMax. Its output is unchanged.

Tests

• TestSafeLineMax: under/at/over the cap, zero means no cap, never splits an escape, counts escaped runes.
• TestSafeLineMaxOutputIsInert: capped output carries no unsafe rune and respects the cap.
• TestRepairReason_CappedTheSameOnDashAndRepair: both sinks print the identical capped string.
• go test ./... green. Local golangci-lint is v2.5.0 and can't load a Go 1.26 config, so CI's lint run is the check.

Closes #506

Release notes

None.

🤖 Generated with Claude Code

https://claude.ai/code/session_01Wfuj7jLb8eNvEHdxurJgt9

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📥 Commits

Reviewing files that changed from the base of the PR and between 3d3dc75 and 9664915.

📒 Files selected for processing (5)

• internal/cli/pr_dash.go
• internal/cli/pr_dash_test.go
• internal/cli/pr_repair.go
• internal/termsafe/termsafe.go
• internal/termsafe/termsafe_test.go

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