Fix layout consistency across all widths

[tmck-code]

Context

Refine the statusline layout so it's consistent and well behaved at all widths. An exhaustive width sweep (40–200, dense 60–130, ascii-mode analysis) surfaced five layout bugs — justify-mode padding asymmetry, misaligned leading numbers, digits flush against borders, ascii-mode pill corners erasing border structure — plus a threshold inconsistency where the plugin row appeared at a narrower width than the context row's rich form. This PR fixes all of them and bumps the version to v0.7.1.

Changes

Justify-mode centering

• The elapsed timer baked left-heavy padding into its string via rjust(8) before layout's fair 50/50 split, leaving it visibly off-center; the value is now centered by the justify pass itself.
• The rebalance also runs when a sibling field consumes all row slack in the same pass (previously still asymmetric at widths 102/112).

Row padding & border adjacency

• Leading numbers on the context-fill and input-token rows now column-align, with reserved width so a value growing 25.9K → 123.0K doesn't shift alignment or touch a border.
• The model section's non-pill branch gained its missing trailing space, so digits never sit flush against the closing border (widths 79–81).

ASCII glyph mode

• Pill corner glyphs mapped to ' ' and could erase structural border elbows/corners; they now map to +.

Width-threshold alignment

• TOKENS_COST_MIN_WIDTH now references MEDIUM_WIDTH (85 → 80 box width), so the rich context row (150.0K (75%) 100%) and the tokens/cost dividers appear from the wide layout's floor — removing the terminal-width 86–90 band where the plugin row showed but the context row stayed degraded.

Checklist

• Tests added or updated for new/changed behaviour
• (bug fixes) a regression test now covers the situation so it can't come back
• N/A — no behaviour change, because:

Screenshots / recording

	before / after
kitchen-sink
justify-108
context-86
model-row-80
ascii-pill-108

• N/A — no visible change

Benchmark

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
main	54.1 ± 7.5	43.4	81.2	1.08 ± 0.19
PR	50.2 ± 5.7	43.2	78.5	1.00

• N/A — no performance-relevant change

System info

Key	Value
OS	Linux archlinux 7.1.5-arch1-1 #1 SMP PREEMPT_DYNAMIC Sun, 26 Jul 2026 00:49:06 +0000 x86_64 GNU/Linux
Claude Code	2.1.233 (Claude Code)
Terminal	TERM=tmux-256color TERM_PROGRAM=tmux SHELL=/bin/bash COLORTERM=truecolor
Locale	LANG=en_AU.UTF-8 LC_ALL=
Python	Python 3.13.13
uv	uv 0.11.32 (3010295ae 2026-07-23 x86_64-unknown-linux-gnu)

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