Move computeSpanDurationMs from human.ts to trace.ts and add shared
utilities for the upcoming span commands: flattenSpanTree, findSpanById,
parseSpanQuery, applySpanFilter, writeSpanTable, and formatSpanDetails.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

The UUID dash-stripping is already handled silently by validateHexId.
Remove the validateAndWarn wrappers, mergeWarnings helper, and all
related warning assertions from tests.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

…ring

Migrate span list/view from imperative output to auto-rendered OutputConfig
pattern, and fix plain-mode ANSI leaks in span tree/ancestor formatting.

**Output system migration (span/list.ts, span/view.ts):**
- Replace `output: "json"` shorthand with `output: { json: true, human: fn, jsonTransform: fn }`
- Extract human formatters (formatSpanListHuman, formatSpanViewHuman) that
  return strings instead of writing to stdout directly
- Extract JSON transforms (jsonTransformSpanList, jsonTransformSpanView) for
  the { data: [...], hasMore } envelope and --fields filtering
- Return `{ data, hint }` from func() so the wrapper handles rendering
- Remove manual `if (flags.json)` branching and direct stdout writes

**Markdown rendering fixes (trace.ts, human.ts):**
- formatAncestorChain: replace raw `muted()` (chalk ANSI) with
  `colorTag("muted", ...)` + `renderMarkdown()` so output respects
  NO_COLOR/isPlainOutput/non-TTY
- formatSimpleSpanTree/formatSpanSimple: replace `muted()` with
  `plainSafeMuted()` that checks `isPlainOutput()` before applying ANSI
- Span list header now renders via `renderMarkdown()` for proper styling

**Formatter exports (trace.ts):**
- Export SPAN_TABLE_COLUMNS for use by span/list formatter
- Add formatSpanTable() return-based wrapper around formatTable()

The orgSlugArb and projectSlugArb generators could produce strings
starting with 'xn--' (punycode-encoded IDN labels). When used as a
subdomain (e.g. 'xn--0a.sentry.io'), the URL constructor silently
decodes the punycode, collapsing the hostname to 'sentry.io' and
dropping the org. This caused flaky failures in the buildTraceUrl →
parseSentryUrl round-trip test.

Fix: filter out xn-- prefixed slugs since real Sentry org/project
slugs are never punycode-encoded.

- Restore null fallback for span_id in formatSpanSimple: span.span_id ?? ''
  (defensive against runtime undefined from normalizeTraceSpan edge cases)
- Unexport SPAN_TABLE_COLUMNS — only used internally by formatSpanTable,
  no external consumers

Use optional chaining (span.span_id?.toLowerCase()) to avoid crash
when a span from the API has neither span_id nor event_id.

UX improvement: Replace --trace flag with positional argument to match
the standardized [<org>/<project>/]<id> pattern used by span list,
trace view, and event view.

Before: sentry span view <span-id> --trace <trace-id>
After:  sentry span view [<org>/<project>/]<trace-id> <span-id>

This is consistent with span list which already uses:
  sentry span list [<org>/<project>/]<trace-id>

SKILL.md: Update placeholder text from generic '<args...>' to
descriptive '<org/project/trace-id...>' and '<trace-id/span-id...>'.

Tests: Add comprehensive tests for both span commands:
- span/list: parsePositionalArgs, parseSort, and func body tests
  (API calls, query translation, org/project resolution) → 86.71% coverage
- span/view: validateSpanId, parsePositionalArgs, and func body tests
  (span lookup, JSON output, multi-span, child tree) → 86.89% coverage
- formatters/trace: findSpanById (case-insensitive, undefined span_id),
  computeSpanDurationMs, spanListItemToFlatSpan

The hint in span list still referenced the removed --trace flag.
Updated to: 'sentry span view <trace-id> <span-id>'

The <project>/<trace-id> format doesn't work because parseSlashSeparatedArg
treats a single-slash input as org/project (missing ID), not project/trace-id.
Unlike span list or trace view, span view can't fall back to two separate args
since the second positional is always a span ID.