fix(pptx): render master/layout, parametric presets, and bulleted lists faithfully

[karthikmudunuri]

Summary

Batch of PPTX import fidelity fixes surfaced while importing the KBC sample deck. Each issue is a real divergence from PowerPoint's rendering, not a cosmetic preference.

Master / canvas

• Honour showMasterSp="0" on <p:sld> / <p:sldLayout> so master decorations don't leak onto title slides that opt out.
• Clip the slide canvas to its 1920×1080 rect — slide-master trim is routinely positioned outside the slide bounds (y=-46px, x=-40px) as bleed marks and would otherwise sit on top of the slide.

Parametric preset shapes

• Synthesise SVG paths for arc, chevron / homePlate / pentagon, cube, and ellipse / circle. Each respects flipH / flipV baked into the path coordinates.
• When the shape carries text (<p:txBody> with content), attach the synthesised path as the text element's backingPath so the silhouette survives the isText short-circuit. Fixes the 7-S diagram's central oval, process-bar chevrons, and 3D-cube grids.
• Apply the inscribed txRect for chevron/homePlate/pentagon so long labels wrap inside the polygon body, not the bounding rectangle. Stops icon-column overlap in process bars.

Bullets and paragraphs

• Surface per-paragraph marL / indent / algn / <a:spcBef> on TextElement and render each paragraph in its own block. Hanging-indent bullets now wrap under the text-after-bullet column instead of collapsing to column 0; spcBef produces the authored vertical air between items.
• Defensive fallback for <a:br/> in paragraphs whose raw XML wasn't preserved — previously "FOO" <br/> "BAR" could collapse into "FOOBAR".
• Resolve <a:fld type="slidenum"> to the slide's 1-based index (was rendering the literal ‹#› design-time token).

Stroke and fill

• Read <a:prstDash> (dot, dash, dashDot, …) on shape strokes and emit border-style / stroke-dasharray. Previously only line-element connectors honoured dashes.
• Parse <a:fillToRect> attributes in their literal-percent form ("0%" / "100%"). PowerPoint emits both that and 1000ths-of-percent integers; Number("0%") = NaN was collapsing radial gradient focus points to 0% 0%.

Connectors

• Apply flipH to <p:cxnSp> and <p:sp prst="line" / "straightConnector1">. Only flipV was honoured before, so flipped-diagonal struts (e.g. 7-S model) drew the wrong way.

Test plan

• Import KBC sample deck end-to-end and verify each slide matches the screenshots reviewed during this work.
• Re-import an existing chart-heavy / placeholder-heavy deck to confirm no regressions in shapes that already rendered correctly.
• Round-trip a slide with bulleted lists (import → edit → export) and confirm marL/indent survive.
• Confirm the canvas clip doesn't crop legitimately on-slide content near the edges.