feat(pnl): group by symbol or magic with uniform group/group_by output

[tanem]

Summary

Phase 3 (part 1) of the read-views-and-reporting expansion (plan; spec sections 3.1/3.2 plus parts of 1.2/1.3). It generalises the pnl grouping dimension.

--by now accepts symbol and magic alongside day|week|month. Time cuts are unchanged — per-account rows plus a combined ALL row per period. symbol and magic instead aggregate across all in-scope accounts, one row per symbol or magic number, with no per-account or ALL row; the first table column becomes SYMBOL/MAGIC and the ACCOUNT column is dropped. Magic groups sort numerically.

Every cut now emits a uniform shape: JSON/CSV rows carry group (the period date, symbol, or magic) and group_by (the --by value), replacing the old period field — a deliberate pre-1.0 break. account is the login for per-account time rows and null/empty for the combined time row and for every symbol/magic row.

Because a symbol/magic cut sums across accounts, it refuses (stderr, exit 1, not silenced by --quiet) when the in-scope accounts span more than one currency — narrow --accounts to a single currency. Internally, aggregate.Row.Period is renamed to Row.Group, the summary is accumulated per-deal so totals are independent of the grouping path, and a new aggregate.AccountsInScope exposes the contributing logins for the currency guard. README and CLAUDE.md are updated.

Built with subagent-driven development: a fresh implementer per task, an independent review after each, and an opus whole-branch review at the end (verdict: ready to merge, no Critical/Important findings).

Test Plan

• go test ./... passes
• CI green across ubuntu/macos/windows (incl. -race) and the lint job
• go vet and staticcheck clean locally
• Time-cut pnl_table.golden byte-identical to main (no regression to existing output)
• New coverage: symbol grouping, magic numeric sort, AccountsInScope range filtering, mixed-currency refusal, empty account columns, dropped ACCOUNT column, new pnl_table_symbol.golden
• pnl --by symbol/magic --format json|csv carries group/group_by and omits per-account/ALL rows (asserted by TestPnLByMagicJSONGroupBy, TestPnLCSVSymbolEmptyAccountColumns)

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 95.91837% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.39%. Comparing base (a0781b7) to head (e799b18).

Files with missing lines	Patch %	Lines
internal/render/render.go	90.69%	4 Missing ⚠️
internal/aggregate/aggregate.go	97.59%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #8      +/-   ##
==========================================
+ Coverage   89.14%   89.39%   +0.24%     
==========================================
  Files          13       13              
  Lines         783      858      +75     
==========================================
+ Hits          698      767      +69     
- Misses         71       76       +5     
- Partials       14       15       +1     

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